Characterization and tRNA recognition of mammalian mitochondrial seryl-tRNA synthetase

Animal mitochondrial protein synthesis systems contain two serine tRNAs (tR NAs(Ser)) corresponding to the codons AGY and UCN, each possessing an unusu al secondary structure; the former lacks the entire D arm, and the latter h as a slightly different cloverleaf structure. To elucidate whether these tw o tRNAs(Ser) can be recognized by the single animal mitochondrial seryl-tRN A synthetase (mt SerRS), we purified mt SerRS from bovine liver 2400-fold a nd showed that it can aminoacylate both of them. Specific interaction betwe en mt SerRS and either of the tRNAs(Ser) was also observed in a gel retarda tion assay. cDNA cloning of bovine mt SerRS revealed that the deduced amino acid sequence of the enzyme contains 518 amino acid residues. The cDNAs of human and mouse mt SerRS were obtained by reverse transcription-polymerase chain reaction and expressed sequence tag data base searches. Elaborate in spection of primary sequences of mammalian mt SerRSs revealed diversity in the N-terminal domain responsible for tRNA recognition, indicating that the recognition mechanism of mammalian mt SerRS differs considerably from that of its prokaryotic counterpart. In addition, the human mt SerRS gene was f ound to be located on chromosome 19q13.1, to which the autosomal deafness l ocus DFNA4 is mapped.