Nucleotide Sequence of the Small Ribosomal RNA Gene from the Mitochondria of Saccharomyces cerevisiae

Abstract

The mitochondrial gene coding for the small rRNA (15S rRNA) of yeast has been isolated and its nucleotide sequence has been determined. A segment of mtDNA carrying the 15S rRNA gene was isolated from a ρ − mutant, strain P2. This ρ − genome has a tandemly repeated unique sequence of 5.5 kbp and carries the genetic markers par R 454 and ts1297 + . The position and orientation of this mtDNA with respect to the wild-type ( ρ + ) mtDNA have been established (Wesolowski et al. 1980). When digested by the restriction endonuclease Hpa II, the mtDNA produced 12 fragments, and two of these fragments (800 bp and 1100 bp) contained sequences homologous to the 15S rRNA sequence. This region of both strands was sequenced after 5′-end labeling and strand separation of various restriction fragments. SEQUENCE OF THE MITOCHONDRIAL 15S rRNA GENE Figure 1 shows the sequence of the 15S rRNA gene and the sequences immediately before and after the gene. Since many regions of this sequence showed obvious homology with the Escherichia coli 16S rRNA sequence, it was aligned with the bacterial sequence. Maximum homology was obtained when some stretches of sequence were considered as additions or deletions with respect to the bacterial sequence: About 44% of the bacterial sequence was homologous to the mitochondrial gene sequence. The mitochondrial sequence contains many internal inverted repeats and can be folded into base-paired structures. Figure 2 shows one of the possible secondary structures of the 15S rRNA, as deduced from the gene sequence. Although this structure may not represent...