Template Activating Factor-I Remodels the Chromatin Structure and Stimulates Transcription from the Chromatin Template
1998; Elsevier BV; Volume: 273; Issue: 51 Linguagem: Inglês
10.1074/jbc.273.51.34511
ISSN1083-351X
AutoresMitsuru Okuwaki, Kyosuke Nagata,
Tópico(s)Animal Virus Infections Studies
ResumoTo study the mechanisms of replication and transcription on chromatin, we have been using the adenovirus DNA complexed with viral basic core proteins, called Ad core. We have identified template activating factor (TAF)-I from uninfected HeLa cells as the factor that stimulates replication and transcription from the Ad core. The nuclease sensitivity assays have revealed that TAF-I remodels the Ad core, thereby making transcription and replication apparatus accessible to the template DNA. To examine whether TAF-I remodels the chromatin consisting of histones, the chromatin structure was reconstituted on the DNA fragment with core histones by the salt dialysis method. The transcription from the reconstituted chromatin was completely repressed, while TAF-I remodeled the chromatin and stimulated the transcription. TAF-I was found to interact with histones. Furthermore, it was shown that TAF-I is capable not only of disrupting the chromatin structure but also of preventing the formation of DNA-histone aggregation and transferring histones to naked DNA. The possible function of TAF-I in conjunction with a histone chaperone activity is discussed. To study the mechanisms of replication and transcription on chromatin, we have been using the adenovirus DNA complexed with viral basic core proteins, called Ad core. We have identified template activating factor (TAF)-I from uninfected HeLa cells as the factor that stimulates replication and transcription from the Ad core. The nuclease sensitivity assays have revealed that TAF-I remodels the Ad core, thereby making transcription and replication apparatus accessible to the template DNA. To examine whether TAF-I remodels the chromatin consisting of histones, the chromatin structure was reconstituted on the DNA fragment with core histones by the salt dialysis method. The transcription from the reconstituted chromatin was completely repressed, while TAF-I remodeled the chromatin and stimulated the transcription. TAF-I was found to interact with histones. Furthermore, it was shown that TAF-I is capable not only of disrupting the chromatin structure but also of preventing the formation of DNA-histone aggregation and transferring histones to naked DNA. The possible function of TAF-I in conjunction with a histone chaperone activity is discussed. base pair(s) cAMP-dependent protein kinase polyvinylidene difluoride polyacrylamide gel electrophoresis bovine serum albumin template activating factor nucleosome assembly protein major late promoter adenovirus major late transcription factor upstream transcription factor. The eukaryotic nucleosome, a unit of chromatin, consists of 146 base pairs (bp)1 of DNA and a histone octamer containing two copies each of histone H2A, H2B, H3, and H4. It has been thought that some modifications of the chromatin structure would be needed before the initiation of replication or transcription (reviewed in Ref. 1Wu C. J. Biol. Chem. 1997; 272: 28171-28174Abstract Full Text Full Text PDF PubMed Scopus (194) Google Scholar). Some factors are shown to gain access to the chromatin DNA directly in vitro (2Workman J.L. Kingston R.E. Science. 1992; 258: 1780-1784Crossref PubMed Scopus (149) Google Scholar), while some others do so with the aid of proteins, such as yeast or human SWI/SNF (reviewed in Refs. 3Peterson C.L. Tamkun J.W. Trends Biochem. Sci. 1995; 20: 143-146Abstract Full Text PDF PubMed Scopus (342) Google Scholar and 4Winston F. Carlson M. Trends Genet. 1992; 8: 387-391Abstract Full Text PDF PubMed Scopus (481) Google Scholar), Drosophila NURF (5Tsukiyama T. Wu C. Cell. 1995; 83: 1011-1020Abstract Full Text PDF PubMed Scopus (511) Google Scholar), and related factors (reviewed in Refs. 6Kadonaga J.T. Cell. 1998; 92: 307-313Abstract Full Text Full Text PDF PubMed Scopus (467) Google Scholar and 7Pazin M.J. Kadonaga J.T. Cell. 1997; 88: 737-740Abstract Full Text Full Text PDF PubMed Scopus (268) Google Scholar), which facilitate the change of interaction between DNA and histone octamer. Furthermore, the gene activity is also regulated by enzymatic modification of histone octamer. Each histone possesses sites in its N-terminal region that can be hyperacetylated, and their acetylation and/or deacetylation are closely related to the gene activity (1Wu C. J. Biol. Chem. 1997; 272: 28171-28174Abstract Full Text Full Text PDF PubMed Scopus (194) Google Scholar, 8Grunstein M. Nature. 1997; 389: 349-352Crossref PubMed Scopus (2370) Google Scholar, 9Hampsey M. Trends Genet. 1997; 13: 427-429Abstract Full Text PDF PubMed Scopus (33) Google Scholar, 10Pazin M.J. Kadonaga J.T. Cell. 1997; 89: 325-328Abstract Full Text Full Text PDF PubMed Scopus (768) Google Scholar, 11Wade P.A. Pruss D. Wolffe A.P. Trends Biochem. Sci. 1997; 22: 128-132Abstract Full Text PDF PubMed Scopus (404) Google Scholar, 12Wolffe A.P. Nature. 1997; 387: 16-17Crossref PubMed Scopus (252) Google Scholar).In order to study the molecular mechanism for activation of transcription and replication from chromatin templates, we have been using the adenovirus DNA complexed with the viral basic core proteins (Ad core) as a model system. The Ad genome is a double-stranded DNA of about 36,000 bp and forms the chromatin-like structure in the virion and in the infected cells. About 200 bp of DNA per viral nucleosome is coiled around six copies of the viral core protein VII, and each unit of viral nucleosome is bridged by the core protein V (13Corden J. Engelking H.M. Pearson G.D. Proc. Natl. Acad. Sci. U. S. A. 1976; 73: 401-404Crossref PubMed Scopus (63) Google Scholar). Immediately after infection, early genes are transcribed, and some of their products together with the host factors NFI, II, and III put forward the genome DNA replication (14Hay R.T. Russell W.C. Biochem. J. 1989; 258: 3-16Crossref PubMed Scopus (36) Google Scholar, 15Stillman B. Annu. Rev. Cell Biol. 1989; 5: 197-245Crossref PubMed Scopus (282) Google Scholar). Newly synthesized DNA does not remain naked but transiently forms a complex with the cellular histones (16Tate V.E. Philipson L. Nucleic Acids Res. 1979; 6: 2769-2785Crossref PubMed Scopus (66) Google Scholar). Late genes are transcribed from the newly replicated DNA, and core proteins and other viral capsid proteins are synthesized. Since histones are not present in the Ad virion, cellular histones on the newly replicated viral DNA are to be removed and replaced with newly synthesized viral core proteins before being packaged into the progeny virus capsid. This type of replacement seems similar to that of histones with protamine during spermatogenesis. Although basic mechanisms for replication and transcription of the Ad genome DNA have been evaluated with in vitro systems using naked DNA templates, in vitro replication and transcription from the Ad core do not take place with the factors needed for these reactions on the naked DNA template (17Leith I.R. Hay R.T. Russell W.C. J. Gen. Virol. 1989; 70: 3235-3248Crossref PubMed Scopus (16) Google Scholar, 18Matsumoto K. Nagata K. Ui M. Hanaoka F. J. Biol. Chem. 1993; 268: 10582-10587Abstract Full Text PDF PubMed Google Scholar, 19Matsumoto K. Okuwaki M. Kawase H. Handa H. Hanaoka F. Nagata K. J. Biol. Chem. 1995; 270: 9645-9650Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar). Since the viral DNA in infected cells is also complexed with either basic viral core proteins or histones to form the chromatin structure, the access oftrans-acting factors involved in replication and transcription to their cognate sites is restricted. Therefore, it is reasonable to presume that the remodeling of the viral chromatin takes place before the initiation of replication and/or transcription.Recently, we have identified from uninfected HeLa cells template activating factor (TAF)-I, which stimulates the replication from the Ad core (18Matsumoto K. Nagata K. Ui M. Hanaoka F. J. Biol. Chem. 1993; 268: 10582-10587Abstract Full Text PDF PubMed Google Scholar). TAF-I also stimulates the transcription from the E1A promoter on the Ad core but not effectively from the major late promoter (MLP) (19Matsumoto K. Okuwaki M. Kawase H. Handa H. Hanaoka F. Nagata K. J. Biol. Chem. 1995; 270: 9645-9650Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar). There are two subtypes of TAF-I, designated as TAF-Iα and TAF-Iβ, both of which have a common amino acid sequence except that N-terminal 30-amino acid sequences are specific for each subtype. TAF-I has a long acidic tail in its C-terminal region that is required for the activation of the Ad core replication and transcription (20Kawase H. Okuwaki M. Miyaji M. Ohba R. Handa H. Ishimi Y. Fujii-Nakata T. Kikuchi A. Nagata K. Genes Cells. 1996; 1: 1045-1056Crossref PubMed Scopus (91) Google Scholar, 21Nagata K. Kawase H. Handa H. Yano K. Yamasaki M. Ishimi Y. Okuda A. Kikuchi A. Matsumoto K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 4279-4283Crossref PubMed Scopus (169) Google Scholar). The stimulatory activity of TAF-Iβ is higher than that of TAF-Iα. TAF-Iβ is the same as the product of theset gene, which is fused to the can gene by the translocation in an acute undifferentiated leukemia (21Nagata K. Kawase H. Handa H. Yano K. Yamasaki M. Ishimi Y. Okuda A. Kikuchi A. Matsumoto K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 4279-4283Crossref PubMed Scopus (169) Google Scholar, 22von Lindern M. van Baal S. Wiegant J. Raap A. Hagemeijer A. Grosveld G. Mol. Cell. Biol. 1991; 12: 3346-3355Crossref Scopus (354) Google Scholar). TAF-I shows low but distinct amino acid sequence homology to nucleosome assembly protein (NAP)-I, which was originally identified as the factor involved in chromatin assembly (23Ishimi Y. Hirosumi J. Sato W. Sugasawa K. Yokota S. Hanaoka F. Yamada M. Eur. J. Biochem. 1984; 142: 431-439Crossref PubMed Scopus (107) Google Scholar). It is indicated that NAP-I can replace for TAF-I in the stimulation of replication and transcription from the Ad core, and that TAF-I has NAP-I activity (20Kawase H. Okuwaki M. Miyaji M. Ohba R. Handa H. Ishimi Y. Fujii-Nakata T. Kikuchi A. Nagata K. Genes Cells. 1996; 1: 1045-1056Crossref PubMed Scopus (91) Google Scholar, 21Nagata K. Kawase H. Handa H. Yano K. Yamasaki M. Ishimi Y. Okuda A. Kikuchi A. Matsumoto K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 4279-4283Crossref PubMed Scopus (169) Google Scholar). Therefore, both proteins are structural and functional homologue of each other.Here we investigate the mechanisms for the stimulation of transcription by TAF-I from both E1A and ML promoters on the Ad core and the reconstituted chromatin consisting of histones. TAF-I stimulates the transcription not only from the E1A promoter on the Ad core but also from the chromatin template reconstituted on the DNA containing the MLP. The nuclease sensitivity assays have revealed that TAF-I stimulates the transcription from these templates by altering core protein-DNA or histone-DNA interaction. Furthermore, the Far Western analyses reveal that TAF-I binds to each core histone and its binding affinity to histone H3/H4 complex is higher than that to H2A/H2B complex. TAF-I binds to core histones through its acidic region and prevents the formation of aggregation between DNA and core histones. Our results lead to the possibility that one of the putative physiological functions of TAF-I may be to suppress the random aggregation of DNA-basic proteins such as DNA-histones. Since other proteins are also identified as histone chaperone, the redundancy of these histone chaperones raises the question how their roles are assigned and cooperated in a cell.DISCUSSIONWe have described the effects of TAF-I on the reconstituted chromatin. TAF-I was originally identified from HeLa cells as the factor that stimulates replication and transcription from the adenovirus DNA-core protein complex in a chromatin-like structure (18Matsumoto K. Nagata K. Ui M. Hanaoka F. J. Biol. Chem. 1993; 268: 10582-10587Abstract Full Text PDF PubMed Google Scholar,19Matsumoto K. Okuwaki M. Kawase H. Handa H. Hanaoka F. Nagata K. J. Biol. Chem. 1995; 270: 9645-9650Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar). Here we have shown that TAF-I also stimulates transcription from the reconstituted chromatin consisting of core histones through the structural change of chromatin. Furthermore, it is shown that TAF-I suppresses random aggregation between DNA and histones.TAF-I remodels the Ad core structure on the E1A promoter region, while it does not have such an effect on the MLP region on the Ad core (Fig.1). In contrast, TAF-I is capable of stimulating the transcription and remodeling the structure of the reconstituted chromatin formed on the DNA fragment containing the MLP (Fig. 4). These results suggest that TAF-I would not have any specificity of DNA sequence, although the MLP on the Ad core is not effectively remodeled by TAF-I. The contradiction of these results would be explained by the difference of the Ad core structure between the E1A promoter and MLP regions. The MLP region may be packed more compactly than E1A promoter region and the MLP in the reconstituted nucleosome. In fact, when the Ad core is used as a template for the transcription, the stimulation of the transcription from the MLP is dependent on the genome DNA replication (19Matsumoto K. Okuwaki M. Kawase H. Handa H. Hanaoka F. Nagata K. J. Biol. Chem. 1995; 270: 9645-9650Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar). It is presumed that the MLP region on the Ad core would be much more insensitive to TAF-I than the E1A promoter region on the Ad core and the MLP in the reconstituted chromatin. Therefore, the structural change of the Ad core within the MLP region coupled with the genome DNA replication would be needed for the transcription from the MLP. In infected cells, the transcription from the MLP is activated dramatically after the onset of the genome DNA replication compared with its transcription activity in early phases of infection. The molecular basis of this transcription switching between early and late phases via replication has not been well clarified. The transcription activation from the MLP by the switch could not be explained simply by the increase of the genome copy number. The Ad genome is complexed with viral basic core proteins in the virion and in the cell during early stages of infection, and newly synthesized DNA would be complexed with histones of host cells and assembled into the chromatin structure following the genome replication (16Tate V.E. Philipson L. Nucleic Acids Res. 1979; 6: 2769-2785Crossref PubMed Scopus (66) Google Scholar). When replication occurs, the Ad core structure is drastically disrupted and trans-acting factors could easily gain access to the parental genome template and/or the newly synthesized DNA. It is suggested that the chromatin structure would be reconstituted on the newly synthesized DNA complexed with transcription factors. Workman et al. (30Workman J.L. Roeder R.G. Kingston R.E. EMBO J. 1990; 9: 1299-1308Crossref PubMed Scopus (98) Google Scholar) demonstrated that the transcription from chromatin reconstituted on the DNA in the presence of MLTF/USF is active, while the transcription from the chromatin template reconstituted without MLTF/USF is repressed. The mechanism of the transcription activation from the MLP bytrans-acting chromatin remodeling factors is the other possibility as we have demonstrated in this study. More precise studies are needed because the transcription level relieved by TAF-I is only 10–20% of that on the naked DNA. These observations raise the possibility that TAF-I may cooperate with other factors in remodeling the chromatin structure in vivo.SWI/SNF, NURF, and other factors that require ATP hydrolysis are suggested to function together with sequence-specific DNA-binding proteins. Recently, Mizuguchi et al. (31Mizuguchi G. Tsukiyama T. Wisniewski J. Wu C. Mol. Cell. 1997; 1: 141-150Abstract Full Text Full Text PDF PubMed Scopus (112) Google Scholar) demonstrated that NURF complexes remodel the chromatin structure and stimulate the transcription dependent on GAL4 fused to HSF. Because the process of the transcription activation from the MLP involves the binding of promoter specific transcription factors such as MLTF/USF, it is possible that the chromatin structure in the MLP region is remodeled by SWI/SNF or NURF-like complexes. Since the DNA fragment used in this study contains the binding sites described above, our system would be useful to further assign roles of these factors. Furthermore, Orphanides et al. (32Orphanides G. LeRoy G. Chang C.H. Luse D.S. Reinberg D. Cell. 1998; 92: 105-116Abstract Full Text Full Text PDF PubMed Scopus (495) Google Scholar) reported that NTP-hydrolysis independent accessory factor, termed FACT, is needed for the elongation step of the transcription from the chromatin templates, although the detailed mechanism of the reaction mediated by FACT is unknown at present. The functional nature of FACT would be different from that of the factors that function as histone chaperone including TAF-I, since FACT cannot remodel the chromatin structure.TAF-I also suppresses the random aggregation of histones, possibly through complex formation with core histones as shown in Figs. 5 and 6. NAP-I and nucleoplasmin and N1/N2 and CAF-I bind preferentially to histones H2A/H2B and histones H3/H4, respectively (reviewed in Ref.33Ito T. Tyler J.K. Kadonaga J.T. Genes Cells. 1997; 2: 593-600Crossref PubMed Scopus (65) Google Scholar). This study showed that TAF-I preferentially interacts with histones H3/H4 rather than H2A/H2B, although more precise experiments under physiological conditions are needed. Since there are a variety of acidic proteins that have the histone binding activity (35Earnshaw W.C. J. Cell Biol. 1987; 105: 1479-1482Crossref PubMed Scopus (106) Google Scholar), the function of each protein and its behavior within a cell should be carefully investigated. In addition, the histone-DNA complex formed by TAF-I would not be a complete chromatin structure. The glycerol gradient assay indicated that the Ad core treated with TAF-I forms the tertiary complex (Fig. 2). Since the mobility of the major nucleoprotein complex in the presence of TAF-I as shown inlane 7 of Fig. 6 was similar to that of the reconstituted chromatin, TAF-I would not be present in the complex. However, it is possible that TAF-I is present in complexes tailing toward the gel origin. It has been reported that NAP-I assembles the chromatin structure cooperatively with ATP-dependent complex (34Ito T. Bulger M. Pazin M.J. Kobayashi R. Kadonaga J.T. Cell. 1997; 90: 145-155Abstract Full Text Full Text PDF PubMed Scopus (519) Google Scholar). It is possible that the nucleoprotein complex formed by TAF-I (Fig. 6) is loosely assembled and another factor would be needed to form the complete chromatin structure. It has been shown that polyanions such as polyglutamic acid and bulk RNA are also able to prevent the random aggregation between DNA and histones, and mediate the histone transfer process (reviewed in Refs. 33Ito T. Tyler J.K. Kadonaga J.T. Genes Cells. 1997; 2: 593-600Crossref PubMed Scopus (65) Google Scholar and 35Earnshaw W.C. J. Cell Biol. 1987; 105: 1479-1482Crossref PubMed Scopus (106) Google Scholar). The internal deletion mutant of TAF-Iβ, which has the same long acidic tail as wild type TAF-Iβ, loses the stimulatory activity for the replication from the Ad core (20Kawase H. Okuwaki M. Miyaji M. Ohba R. Handa H. Ishimi Y. Fujii-Nakata T. Kikuchi A. Nagata K. Genes Cells. 1996; 1: 1045-1056Crossref PubMed Scopus (91) Google Scholar), suggesting that not only acidity but also the proper conformation of the acidic region in TAF-I is required for its activity.The function of TAF-I in vivo is unknown. It is reported that components of SWI/SNF complex are enriched in the active chromatin and nuclear matrix fractions (36Reyes J.C. Muchardt C. Yaniv M. J. Cell Biol. 1997; 137: 263-274Crossref PubMed Scopus (200) Google Scholar). From the fact that TAF-I has been originally purified from cytoplasm fractions, TAF-I seems to leaked out easily from the nucleus, although TAF-I has a nuclear localization signal and it is retained in the nucleus in part through its acidic region (29Nagata K. Saito S. Okuwaki M. Kawase H. Furuya A. Hanai N. Okuda A. Kikuchi A. Exp. Cell Res. 1998; 240: 274-281Crossref PubMed Scopus (104) Google Scholar). It is an open question how the TAF-I activities for disruption of the chromatin structure and prevention of random aggregation between DNA and histones are controlled in a cell. Since the level of TAF-I proteins are not significantly fluctuated through the cell cycle (29Nagata K. Saito S. Okuwaki M. Kawase H. Furuya A. Hanai N. Okuda A. Kikuchi A. Exp. Cell Res. 1998; 240: 274-281Crossref PubMed Scopus (104) Google Scholar), qualitative change rather than quantitative change would be needed. It is tentatively speculated that some modifications may operate in the regulation of the TAF-I activity. Recently, it has been reported that Xenopus TAF-Iβ homologue specifically binds to a B-type cyclin (37Kellogg D.R. Kikuchi A. Fujii-Nakata T. Turck C.W. Murray A.W. J. Cell Biol. 1995; 130: 661-673Crossref PubMed Scopus (158) Google Scholar). Human TAF-I is found to inhibit the activity of protein phosphatase 2A (38Li M. Makkinje A. Damuni Z. J. Biol. Chem. 1996; 271: 11059-11062Abstract Full Text Full Text PDF PubMed Scopus (402) Google Scholar) by the multi-protein complex formation (39Adler H.T. Nallaseth F.S. Walter G. Tkachuk D.C. J. Biol. Chem. 1997; 272: 28407-28414Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar). Based on these facts, the TAF-I activity is possibly regulated during the cell cycle by phosphorylation and/or TAF-I may regulate phosphorylation/dephosphorylation. On this line, TAF-Iβ has shown to be phosphorylated in vivo in its N-terminal region (40Adachi Y. Pavlakis G.N. Copeland T.D. FEBS Lett. 1994; 340: 231-235Crossref PubMed Scopus (46) Google Scholar), although a specific kinase(s) that phosphorylates TAF-I is unknown. From these observations, TAF-I would be a multi-functional protein. The eukaryotic nucleosome, a unit of chromatin, consists of 146 base pairs (bp)1 of DNA and a histone octamer containing two copies each of histone H2A, H2B, H3, and H4. It has been thought that some modifications of the chromatin structure would be needed before the initiation of replication or transcription (reviewed in Ref. 1Wu C. J. Biol. Chem. 1997; 272: 28171-28174Abstract Full Text Full Text PDF PubMed Scopus (194) Google Scholar). Some factors are shown to gain access to the chromatin DNA directly in vitro (2Workman J.L. Kingston R.E. Science. 1992; 258: 1780-1784Crossref PubMed Scopus (149) Google Scholar), while some others do so with the aid of proteins, such as yeast or human SWI/SNF (reviewed in Refs. 3Peterson C.L. Tamkun J.W. Trends Biochem. Sci. 1995; 20: 143-146Abstract Full Text PDF PubMed Scopus (342) Google Scholar and 4Winston F. Carlson M. Trends Genet. 1992; 8: 387-391Abstract Full Text PDF PubMed Scopus (481) Google Scholar), Drosophila NURF (5Tsukiyama T. Wu C. Cell. 1995; 83: 1011-1020Abstract Full Text PDF PubMed Scopus (511) Google Scholar), and related factors (reviewed in Refs. 6Kadonaga J.T. Cell. 1998; 92: 307-313Abstract Full Text Full Text PDF PubMed Scopus (467) Google Scholar and 7Pazin M.J. Kadonaga J.T. Cell. 1997; 88: 737-740Abstract Full Text Full Text PDF PubMed Scopus (268) Google Scholar), which facilitate the change of interaction between DNA and histone octamer. Furthermore, the gene activity is also regulated by enzymatic modification of histone octamer. Each histone possesses sites in its N-terminal region that can be hyperacetylated, and their acetylation and/or deacetylation are closely related to the gene activity (1Wu C. J. Biol. Chem. 1997; 272: 28171-28174Abstract Full Text Full Text PDF PubMed Scopus (194) Google Scholar, 8Grunstein M. Nature. 1997; 389: 349-352Crossref PubMed Scopus (2370) Google Scholar, 9Hampsey M. Trends Genet. 1997; 13: 427-429Abstract Full Text PDF PubMed Scopus (33) Google Scholar, 10Pazin M.J. Kadonaga J.T. Cell. 1997; 89: 325-328Abstract Full Text Full Text PDF PubMed Scopus (768) Google Scholar, 11Wade P.A. Pruss D. Wolffe A.P. Trends Biochem. Sci. 1997; 22: 128-132Abstract Full Text PDF PubMed Scopus (404) Google Scholar, 12Wolffe A.P. Nature. 1997; 387: 16-17Crossref PubMed Scopus (252) Google Scholar). In order to study the molecular mechanism for activation of transcription and replication from chromatin templates, we have been using the adenovirus DNA complexed with the viral basic core proteins (Ad core) as a model system. The Ad genome is a double-stranded DNA of about 36,000 bp and forms the chromatin-like structure in the virion and in the infected cells. About 200 bp of DNA per viral nucleosome is coiled around six copies of the viral core protein VII, and each unit of viral nucleosome is bridged by the core protein V (13Corden J. Engelking H.M. Pearson G.D. Proc. Natl. Acad. Sci. U. S. A. 1976; 73: 401-404Crossref PubMed Scopus (63) Google Scholar). Immediately after infection, early genes are transcribed, and some of their products together with the host factors NFI, II, and III put forward the genome DNA replication (14Hay R.T. Russell W.C. Biochem. J. 1989; 258: 3-16Crossref PubMed Scopus (36) Google Scholar, 15Stillman B. Annu. Rev. Cell Biol. 1989; 5: 197-245Crossref PubMed Scopus (282) Google Scholar). Newly synthesized DNA does not remain naked but transiently forms a complex with the cellular histones (16Tate V.E. Philipson L. Nucleic Acids Res. 1979; 6: 2769-2785Crossref PubMed Scopus (66) Google Scholar). Late genes are transcribed from the newly replicated DNA, and core proteins and other viral capsid proteins are synthesized. Since histones are not present in the Ad virion, cellular histones on the newly replicated viral DNA are to be removed and replaced with newly synthesized viral core proteins before being packaged into the progeny virus capsid. This type of replacement seems similar to that of histones with protamine during spermatogenesis. Although basic mechanisms for replication and transcription of the Ad genome DNA have been evaluated with in vitro systems using naked DNA templates, in vitro replication and transcription from the Ad core do not take place with the factors needed for these reactions on the naked DNA template (17Leith I.R. Hay R.T. Russell W.C. J. Gen. Virol. 1989; 70: 3235-3248Crossref PubMed Scopus (16) Google Scholar, 18Matsumoto K. Nagata K. Ui M. Hanaoka F. J. Biol. Chem. 1993; 268: 10582-10587Abstract Full Text PDF PubMed Google Scholar, 19Matsumoto K. Okuwaki M. Kawase H. Handa H. Hanaoka F. Nagata K. J. Biol. Chem. 1995; 270: 9645-9650Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar). Since the viral DNA in infected cells is also complexed with either basic viral core proteins or histones to form the chromatin structure, the access oftrans-acting factors involved in replication and transcription to their cognate sites is restricted. Therefore, it is reasonable to presume that the remodeling of the viral chromatin takes place before the initiation of replication and/or transcription. Recently, we have identified from uninfected HeLa cells template activating factor (TAF)-I, which stimulates the replication from the Ad core (18Matsumoto K. Nagata K. Ui M. Hanaoka F. J. Biol. Chem. 1993; 268: 10582-10587Abstract Full Text PDF PubMed Google Scholar). TAF-I also stimulates the transcription from the E1A promoter on the Ad core but not effectively from the major late promoter (MLP) (19Matsumoto K. Okuwaki M. Kawase H. Handa H. Hanaoka F. Nagata K. J. Biol. Chem. 1995; 270: 9645-9650Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar). There are two subtypes of TAF-I, designated as TAF-Iα and TAF-Iβ, both of which have a common amino acid sequence except that N-terminal 30-amino acid sequences are specific for each subtype. TAF-I has a long acidic tail in its C-terminal region that is required for the activation of the Ad core replication and transcription (20Kawase H. Okuwaki M. Miyaji M. Ohba R. Handa H. Ishimi Y. Fujii-Nakata T. Kikuchi A. Nagata K. Genes Cells. 1996; 1: 1045-1056Crossref PubMed Scopus (91) Google Scholar, 21Nagata K. Kawase H. Handa H. Yano K. Yamasaki M. Ishimi Y. Okuda A. Kikuchi A. Matsumoto K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 4279-4283Crossref PubMed Scopus (169) Google Scholar). The stimulatory activity of TAF-Iβ is higher than that of TAF-Iα. TAF-Iβ is the same as the product of theset gene, which is fused to the can gene by the translocation in an acute undifferentiated leukemia (21Nagata K. Kawase H. Handa H. Yano K. Yamasaki M. Ishimi Y. Okuda A. Kikuchi A. Matsumoto K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 4279-4283Crossref PubMed Scopus (169) Google Scholar, 22von Lindern M. van Baal S. Wiegant J. Raap A. Hagemeijer A. Grosveld G. Mol. Cell. Biol. 1991; 12: 3346-3355Crossref Scopus (354) Google Scholar). TAF-I shows low but distinct amino acid sequence homology to nucleosome assembly protein (NAP)-I, which was originally identified as the factor involved in chromatin assembly (23Ishimi Y. Hirosumi J. Sato W. Sugasawa K. Yokota S. Hanaoka F. Yamada M. Eur. J. Biochem. 1984; 142: 431-439Crossref PubMed Scopus (107) Google Scholar). It is indicated that NAP-I can replace for TAF-I in the stimulation of replication and transcription from the Ad core, and that TAF-I has NAP-I activity (20Kawase H. Okuwaki M. Miyaji M. Ohba R. Handa H. Ishimi Y. Fujii-Nakata T. Kikuchi A. Nagata K. Genes Cells. 1996; 1: 1045-1056Crossref PubMed Scopus (91) Google Scholar, 21Nagata K. Kawase H. Handa H. Yano K. Yamasaki M. Ishimi Y. Okuda A. Kikuchi A. Matsumoto K. Proc. Natl. Acad. Sci. U. S. A.
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