Formation of the 3' end of yeast mitochondrial mRNAs occurs by site-specific cleavage two bases downstream of a conserved dodecamer sequence.

Mitochondrial mRNAs in yeast arise by processing of polygenic primary transcripts at a conserved dodecamer sequence (5'-AAUAAPyAUUCUU-3'). Previous results indicated that processing at dodecamer sites interrupted the sequence implying that it functioned primarily as a signal for 3' end formation of mRNAs. We have determined the precise cleavage site for RNAs processed at the dodecamer sequences associated with the oli1 gene and the omega intron of the 21S rRNA gene. In both cases cleavage occurred two bases downstream of the site. Hydrolysis left the PO4 group attached to the 3' terminus of the cleavage products. These results demonstrate for the first time that mature mitochondrial mRNAs terminate with an intact dodecamer sequence. In light of the recent identification of a protein complex within mitochondria that binds to RNAs terminating with an intact dodecamer sequence, these results support the idea that the dodecamer sequence functions not only within pre-mRNAs as a processing site, but within mature mRNAs as well, possibly for the stabilization and/or translation.