Nucleotide sequence of the mitochondrial cytochrome oxidase subunit II gene in the yeast Hansenula saturnus.

Abstract

The gene for subunit II of cytochrome oxidase in the yeast Hansenula saturnus was previously shown to be located on a 1.7 kb HindIII-BamHI fragment of mitochondrial DNA (Lawson and Deters, accompanying paper). In this paper, we report the nucleotide sequence of a large part of this fragment, covering the coding region of the subunit II gene, designated coxII, and its 5' and 3' flanking regions. The coding region of the coxII gene consists of a continuous open reading frame, 744 nucleotides long, containing 6 in frame TGA codons. Examination of the sequence and alignment with known homologous gene sequences of other organisms indicates that TGA codes for tryptophan in H. saturnus mitochondria as it does in several other mitochondria. Despite considerable homology to subunit II of Saccharomyces cerevisiae, there are 9 codons used in coxII that are not used in the corresponding S. cerevisiae gene. CTT, which is believed to code for threonine in S. cerevisiae mitochondria, appears 3 times in coxII and probably codes for leucine. While the CGN family is rarely, if ever, used in S. cerevisiae mitochondria, CGT appears 4 times in coxII and probably codes for arginine. The deduced amino acid sequence, excluding the first ten amino acids at the N-terminus, is 81% homologous to the amino acid sequence of the S. cerevisiae subunit II protein. The first ten amino acids at the N-terminus are not homologous to the N-terminus of the S. cerevisiae protein but are highly homologous to the first ten amino acids of the deduced amino acid sequence of subunit II of Neurospora crassa. Minor variations of a transcription initiation signal and an end of message or processing signal reported in S. cerevisiae are found in the regions flanking the H. saturnus coxII gene. The subunit II gene contains numerous symmetrical elements, i.e. palindromes, inverted repeats, and direct repeats. Some of these have conserved counterparts in the S. cerevisiae subunit II gene, suggesting that they may be functionally or structurally important.