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The synthesis of nucleic acids and proteins in the nuclei of Tradescantia root tips

1959; Elsevier BV; Volume: 16; Issue: 3 Linguagem: Inglês

10.1016/0014-4827(59)90128-4

1090-2422

Jesse E. Sisken,

Protist diversity and phylogeny

An autoradiographic and isotopic study was made of the synthesis of DNA, RNA and some nuclear proteins in root tip nuclei of Tradescantia. 1. During the growth of the nucleus in early interphase, there is no incorporation of tritium labelled thymidine into DNA. After a nucleus reaches a certain size, however, there is incorporation into DNA with little or no further increase in nuclear volume. 2. The incorporation of orotic acid-14C into both RNA and DNA of the same nucleus was studied. A plot of incorporation into RNA against incorporation into DNA for a short exposure to isotope (6 hours) shows an inverse relationship. This was interpreted to mean that the two nucleic acids are not synthesized together. 3. A similar plot for a long term exposure (12 hours) is interpreted to mean that the peak of RNA synthesis occurs prior to DNA synthesis. However, a small amount of incorporation was found to take place after DNA synthesis. 4. The plot of incorporation of orotic acid-14C into RNA of those cells with no incorporation into DNA in the short term experiment indicates that RNA is being synthesized when an increase in volume of the nucleus occurs. Since the thymidine experiments showed no incorporation into DNA during increase in nuclear volume, this is an additional, independent indication of the validity of the concept that most of the RNA synthesis occurs before DNA synthesis in this material. 5. Under the conditions of this experiment, it takes a cell at least eight hours to go from the end of DNA synthesis to prophase and prophase to telophase takes approximately two hours. 6. The incorporation of lysine-14C into nuclear proteins which are not removed by the Feulgen hydrolysis was studied. Since after a six hour exposure to isotope, nuclei of all volumes and stages of division appeared to be labelled, both in chromatin and nucleolus when present, it was concluded that protein synthesis probably occurs in all stages of the cell cycle.