BIOGENESIS OF MITOCHONDRIA .53. PHYSICAL MAP OF GENETIC-LOCI IN THE 21S RIBOSOMAL-RNA REGION OF MITOCHONDRIAL-DNA IN SACCHAROMYCES-CEREVISIAE

The mitochondrial DNA (mtDNA) of sevcral petite mutants of Saccharomyces cerevisiae characterized for the loss or retention of genetic loci in the region of the 21S rRNA gene has been analysed. RNA-DNA hybridization has indicated the presence of deletions within the 21S rRNA gene of some of these petites. The positions of the deletions were mapped precisely using the restriction enzymes HpaII, HaeIII and SalI. The results permitted the determination of the restriction sites relative to the 21S rRNA gene. By comparing the retention and loss of genetic loci with the mtDNA sequences present in each petite, physical map positions for the ery1, tsr1 and ω loci were assigned within the 21S rRNA gene. However, the data for the cap1 locus did not permit an unambiguous assignment of this locus inside or outside of the 21S rRNA gene. In some petites deleted for the tsr1 locus the behaviour of the ω locus underwent a change from {ie307-1}.to {ie307-2}, and this was shown to be accompanied by a deletion of 1.5 Kbp from within the 21S rRNA gene. The interference from this observation is that {ie307-3} behaviour can arise by deletion of sequences from {ie307-4}. This contrasts with the previously published observations that {ie307-5} strains contain an inserted sequence of about 1 Kbp that is not present in {ie307-6} strains. The rationalization of this apparent contradiction is that ω behaviour is not necessarily determined by a particular short nucleotide sequence, but rather, ω action reflects in some way the sum total of sequences retained or lost in this region of mtDNA. © 1979 Springer-Verlag.