IN-VIVO ANALYSIS OF SEQUENCES REQUIRED FOR TRANSLATION OF CYTOCHROME-B TRANSCRIPTS IN YEAST MITOCHONDRIA

Respiratory chain proteins encoded by the yeast mitochondrial genome a re synthesized within the organelle, Mitochondrial mRNAs lack a 5' cap structure and contain long AU-rich 5' untranslated regions (UTRs) wit h many potential translational start sites and no apparent Shine-Dalga rno-like complementarity to the 15S mitochondrial rRNA. However, trans lation initiation requires specific interactions between the 5' UTRs o f the mRNAs, mRNA-specific activators, and the ribosomes. In an initia l step toward identifying potential binding sites for the mRNA-specifi c translational activators and the ribosomes, we have analyzed the eff ects of deletions in the 5' UTR of the mitochondrial COB gene on trans lation of COB transcripts in vivo. The deletions define two regions of the COB 5' UTR that are important for translation and indicate that s equence just 5' of the AUG is involved in selection of the correct sta rt codon. Taken together, the data implicate specific regions of the 5 ' UTR of COB mRNA as possible targets for the mitochondrial translatio nal machinery.