Primary structure of wild-type and mutant alleles of the PET494 gene of Saccharomyces cerevisiae.

The product of the yeast nuclear gene PET494 is required specifically for the translation of the mitochondrially encoded subunit III of cytochrome c oxidase. We have determined the DNA sequence of a 1.9 kb fragment carrying PET494. The sequence contains a single long open reading frame of 489 codons. This open reading frame encodes the PET494 protein since the DNA sequence of the corresponding fragment derived from a strain with a known pet494 amber mutation contained an in frame UAG codon. The results of S1 nuclease protection experiments demonstrated that this region is transcribed and that the 5' ends of the major transcripts lie 30 to 40 base-pairs upstream of the first AUG codon in the PET494 reading frame. The predicted PET494 protein has a highly basic amino-terminal domain of 66 amino acids followed by a stretch of 32 uncharged residues, half of which are hydrophobic. The remainder of the protein is not unusual in amino acid composition or distribution except that the carboxyterminal region is notably basic. The phenotype of mutations generated in vitro around codon 119 by exonuclease digestion and linker insertion indicated that this region is dispensable for function. A mutation caused by deletion of 101 bp of coding sequence behaved like a simple frameshift when inserted into the chromosome: it was partially suppressed by the recessive non-group specific frameshift suppressor suf13 and reverted to Pet+ phenotype by mutations linked to PET494.