SUBUNIT-6 OF THE F-O-ATP SYNTHASE COMPLEX FROM CYTOPLASMIC MALE-STERILE RADISH - RNA EDITING AND NH2-TERMINAL PROTEIN SEQUENCING

RNA editing and NH2-terminal processing of subunit 6 (atp6) of the mit ochondrial F-o-ATPase complex has been investigated for the normal (fe rtile) and Ogura (male-sterile) radish cytoplasms to determine if prev iously identified differences between the Ogura atp6 locus and its nor mal radish counterpart are associated with cytoplasmic male sterility. Analysis of cDNA clones from five different sterile and fertile radis h lines identified one C-to-U transition, which results in the replace ment of a proline with a serine, in several of the lines. No editing o f atp6 transcripts was observed in two lines, Scarlet Knight (normal r adish) and sterile CrGC15 (Ogura radish). This is the first example of a naturally occurring plant mitochondrial gene that is not edited. Th e Ogura atp6 polypeptide is synthesized with a predicted NH2-terminal extension of 174 amino acids in contrast to the nine amino acid extens ion found in normal radish. In spite of the lack of similarity between the two extensions, NH2-terminal sequence analysis indicates that bot h polypeptides are processed to yield identical core proteins with a s erine as the NH2-terminal residue. These results indicate that ATPase subunit 6 is synthesized normally in Ogura radish, and that it is unli kely that the atp6 locus is associated with Ogura cytoplasmic male ste rility.