Portal de Periódicos da CAPES

Origins of transcripts of the yeast mitochondrial var 1 gene.

1984; Elsevier BV; Volume: 259; Issue: 9 Linguagem: Inglês

10.1016/s0021-9258(18)91116-6

1083-351X

Hans Peter Zassenhaus, Nicola Martin, Ronald A. Butow,

Fungal and yeast genetics research

Transcription of the yeast mitochondrial varl gene encoding the mitochondrial small ribosomal subunit protein, varl, has been examined in wild type and petite strains by Northern hybridization, S1 nuclease protection experiments, and analysis of primary transcripts by in vitro labeling of mitochondrial RNAs with [cY-~*P]GTP and guanylyl transferase.We have identified a transcription unit in which a polycistronic precursor gives rise to the mRNAs for ATPase subunit 9 (the product of the olil gene), varl, and tRNA&.Potential cleavage sites have been identified within this precursor that separates olil, tRNA&, and varl transcripts.Transcriptional initiation of the polycistronic precursor occurs from one of two nearby copies of the sequence, 5'-ATATAAGTA-3', located approximately 550 and 630 base pairs 5' to the olil gene.A closely related sequence, 5'-TTATAAGTA-3', is found within the varl gene and may serve as a transcriptional initiation site for one of a pair of primary transcripts detected in a petite retaining the varl/40.0]allele.The other primary transcript in this strain initiates upstream in a region of the varl gene containing no recognizable initiation sites. ~~ ~Transcriptional analysis of the yeast mitochondrial genome suggests that most primary gene transcripts are synthesized as larger precursors that undergo processing to give the mature RNAs.For example, the mature 21 S rRNA is generated by 3' processing of larger precursors (1,2) whereas the mature 15 S rRNA is generated by 5' cleavages of a 15.5 S precursor (3-5).Those yeast genes containing introns (cob, encoding the cytochrome b apoprotein, oxi-3, encoding subunit I of cytochrome oxidase, and the a+ allele of the 21 S rRNA gene) exhibit RNA precursors that undergo splicing (6-8).In addition, the cob and oxi-3 mosaic genes required intron-encoded proteins (maturases) for splicing of some of their intervening sequences (9-11).Mature mitochondrial tRNAs also appear to be generated from larger precursors, with correct 5' processing dependent upon the trans-acting product of the "tRNA synthesis" locus, a region of the mitochondrial genome located between the tRNAyand tRNAPr" genes (12,13).Any proteins necessary for maturation of the 5' and 3' ends of tRNAs are encoded in the nucleus since these activities can occur in petites.For the remaining protein genes (all nonmosaic), of' Health and the Robert A.