Molecular characterization of a mitochondrial mutant carrying point mutations in the 3 untranslated region of the COX3 mRNA from Saccharomyces cerevisiae

Abstract

The COX3 gene is located in the mitochondrial genome and encodes the cytochrome c oxidase subunit III of the respiratory chain in yeast. In addition to an 810-bases-coding region, the COX3 mRNA has a 613-bases 5 untranslated region (UTR) and an approximately 2.2-kb 3UTR. Studies on the expression of COX3 have shown that the COX3 5UTR sequences are involved in the translation initiation of the COX3 mRNA. However, the function of the COX3 3UTR in gene expression is unknown. In this study, we report molecular characteristics of a mitochondrial cox3 mutant, M9-3, with alterations in the COX3 3UTR. We found that COX3 mRNA levels in M9-3 are comparable to those in its wild-type parent strain. But we found that levels of subunit III, the COX3 gene product, are reduced in M9-3 relative to its wild-type. Together, these observations suggest a possible role for the COX3 3UTR sequences in the subunit III synthesis.