volume 10 Number 221982 Nucleic Ac ids Research Transcripts of mitochondrial tRNA genes in Saccharomyces cerevisiae

TFe transcription of a group of tRNA genes from the large tRNA gene cluster of mitochondrial DNA from Saccharomyces cerevisiae hase been invest^ gated by hybridization with DNA probes carrying tRNA coding sequences and small portions of the A+T rich intergenicregions. 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, car-rying 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 1J_ mited amount. The low molecular weight transcripts were analysed by the SI mapping technique and found to include both a tRNA sequence and the upstream 51 flanking region extending as far as the 31 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