The putative mRNA for subunit II of human cytochrome c oxidase starts directly at the translation initiator codon.

The gene for subunit II of cytochrome c oxidase (COII) in human mitochondrial DNA (mtDNA) is immediately contiguous, on its 5'-end side, to a tRNAAsp gene. Since all eukaryotic mRNAs so far analysed have been shown to have a noncoding stretch, which is presumably used for ribosome attachment on the 5'-side of the coding sequence, it was resonable to ask whether, in the case of the human COII mRNA, the above function is performed by the tRNAAsp sequence or a portion of it, or whether this mRNA lacks a 5' noncoding stretch. We have sequenced a 5'-end proximal segment of the putative COII mRNA from HeLa cells of about 30 nucleotides and have aligned it with the COII coding sequence in human mtDNA. Our results show that this RNA starts directly at the AUG initiator codon.