Expression of the oxi1 and maturase-related RF1 genes in yeast mitochondria.

Transcription of the yeast mitochondrial oxi1 gene (cytochrome oxidase subunit 2) is initiated at a variant non anucleotide sequence, TTAAAAGTA, located 54 bp upstream from the protein-coding gene. Transcriptional initiation at this site gives rise to a 2,500 nucleotide primary transcript containing both the oxi1 gene and the downstream maturase-related reading frame, RF1. Precise transcript mapping has revealed that the 3'-end of the mature oxi1 mRNA is generated by an endonucleolytic cleavage which takes place after the conserved dodecamer sequence, AAUAAUAUUCUU (End-of-Messenger signal), 75 nucleotides downstream from the oxi1 stop codon. Since the RF1 5'-terminal coding region overlaps the oxi1 3'-terminal coding sequence, cleavage at this motif truncates the RF1 message suggesting that the expression of the putative RF1 protein is controlled at the level of dodecamer processing.