TRANSFER-RNA EDITING IN LAND SNAIL MITOCHONDRIA

Some mitochondrial tRNA genes of land snails show mismatches in the ac ceptor stems predicted from their gene sequences. The majority of thes e mismatches fall in regions where the tRNA genes overlap with adjacen t down-stream genes. We have synthesized cDNA from four circularized t RNAs and determined the sequences of the 5' and 3' parts of their acce ptor stems. Three of the four tRNAs differ from their corresponding ge nes at a total of 13 positions, which all fall in the 3' part of the a cceptor stems as well as the discriminator bases. The editing events d etected involve changes from cytidine, thymidine, and guanosine to ade nosine residues, which generally restore base-pairing in the stems. Ho wever, in one case an A-A mismatch is created from an A-C mismatch. It is suggested that this form of RNA editing may involve polyadenylylat ion of the maturing tRNAs as an intermediate.