Transcripts of mitochondrial tRNA genes inSaccharomyces cerevisiae

Abstract

The transcription of a group of tRNA genes from the large tRNA gene cluster of mitochondrial DNA from Saccharomyces cerevisiae hase been investi gated by hybridization with DNA probes carrying t coding sequences and small portions of the A+T rich intergenic regions.Results have shown that in some rho mutants (DS502, Fll) mature tRNA was absent, but a few transcripts could be detected. Some high molecular weight species actually hybridized with DNA probes carrying different tRNA coding sequences. Low molecular weight transcripts (100-150 nucleotides, carrying one tRNA sequence) were also present in these mutants. A high molecular weight transcript was also observed in the wild type, though in much more 1i mited amount. The low molecular weight transcripts were analysed by the Sl mapping technique and found to include both a tRNA sequence and the upstream 5' flanking region extending as far as the 3' end of the preceding tRNA gene.The results suggest the existence of a common transcript bearing sever al tRNA sequences and indicate a possible mechanism of processing, which might be defective in mutants.

Expression of the clustered mitochondrial tRNA genes in Saccharomyces cerevisiae: transcription and processing of transcripts.

“…The first (very faint) signal (indicated by an open circle in Figure 4, lane 11) corresponded to a transcript terminating at the 3' end of the tRNAArg gene, while the second (very strong one, indicated by a dot in Figure 4, slot 11 and 13) corresponded to a transcript terminating at the 3' end of the tRNALys gene. A diagrammatic representation of the transcripts mapped in these and previous experiments (Frontali et al, 1982) is shown in Figure 5. Figure 2, 3 and 6a).…”

“…Lanes were as follows: (1) The smallest transcript (130 nucleotides), which has not been detected in w.t. cells, has previously been shown to contain the sequence of tRNAHis and the upstream intergenic sequence up to the 3' end of the preceding tRNAcys gene (Frontali et al, 1982).…”

“…Preparation and labelling of nucleic acids Mitochondrial DNA and RNA were prepared from purified mitochondria as previously reported (Frontali et al, 1982). For the preparation of 5' end-labelled single-stranded probes, mtDNA from strains DS502 or DS504 was treated with Hinji (Biolab) or TaqI (Biolab) restriction endonuclease, respectively, followed by treatment with calf intestine phosphatase (Boehringer, 2 U/sg of DNA).…”

RNase P activity in the mitochondria of Saccharomyces cerevisiae depends on both mitochondrion and nucleus-encoded components.

“…Mitochondrial DNA deletion mutants that lack this locus accumulate tRNA precursors (6,11,23,24). Characterization of tRNA gene transcripts in such mutants shows that they are correctly processed on the 3' end but retain 5' tRNA precursor leader sequences (13).…”

“…Transcript mapping shows that other 5' tRNA leaders result from cleavage events that separate precursors * Corresponding author. from polycistronic RNA molecules (6,20,24). tRNA precursors of both origins require the tRNA synthesis locus for 5' leader processing (23).…”