Transcripts of mitochondrial tRNA genes in Saccharomyces cerevisiae.

The transcription of a group of tRNA genes from the large tRNA gene cluster of mitochondrial DNA from Saccharomyces cerevisiae has been investigated by hybridization with DNA probes carrying tRNA coding sequences and small portions of the A + T rich intergenic regions. Results have shown that in some rho- mutants (DS502, F11) 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 limited amount. The low molecular weight transcripts were analysed by the S1 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 several tRNA sequences and indicate a possible mechanism of processing, which might be defective in mutants.