Location of transcriptional control signals and transfer RNA sequences in Torulopsis glabrata mitochondrial DNA

Abstract

Determination of sequences from the nine regions separating the large genes in the 19-kbp mitochondrial DNA from Torulopsis glabrata has led to the identification of 23 tRNA genes and to the recognition of two types of short repeated sequence implicated in mitochondrial genome expression. The two short repeated sequences are a nonanucleotide motif, 5'-TATAAGTAA-3' and a dodecanucleotide motif, 5'-TATAATATTCTT-3'. By RNA sequence determination it has been found that primary transcripts of the small and large rRNAs commence at the 3' penultimate adenine of the nonanucleotide sequence. This motif has also been found in the DNA sequence upstream from f-methionine, phenylalanine, leucine, tyrosine and glycine tRNAs, cytochrome oxidase subunit 2 and ATPase subunit 9. The dodecanucleotide sequence is found at least once in each of the nine regions between the large genes. Determination of the 3' ends of the small and large rRNAs has shown their location to be 8 and 23 nucleotides downstream from the dodecanucleotide sequence. This motif is thought to be involved in signalling processing of polycistronic transcripts. Such transcripts are invoked to account for the production of mRNAs for cytochrome b, cytochrome oxidase subunits 1 and 3, and the joint mRNA for ATPase subunits 8 and 6 genes that lack an adjacent upstream nonanucleotide transcription initiation signal sequence. Processing of polycistronic transcripts at tRNA sequences is also implicated in the formation of mature mRNAs. From the position of tRNA genes relative to the nonanucleotide motif it appears that clusters of these genes are co-transcribed with downstream sequences for cytochrome oxidase subunits 1 and 3.