Biochemical and genetic approaches to the study of mammalian mitochondrial tRNAs

The possible existence of mammalian mitochondrial asparaginyl-tRNA has been examined using a variety of approaches. [3H]Asparagine was incorporated into protein by mitochondria of the Chinese hamster ovary (CHO) cell line Asn-7, which has a temperature-sensitive cytosolic asparaginyl-tRNA synthetase, either in the presence of cycloheximide or at a nonpermissive temperature. Isolated mitochondria of CHO thymidine kinase minus (TK-) cells also incorporated the amino acid into protein. In each case, the number and electrophoretic mobility of the proteins was the same as mitochondrially synthesized proteins of CHO TK- cells labelled with [35S]methionine. A tRNAAsn could be charged in isolated CHO TK- cell mitochondria and the asparaginyl-tRNA was found to elute before its cytosolic counterpart on an RPC-5 column and to have a higher mobility on polyacrylamide slab gels run under denaturing conditions. This is the first demonstration of a unique mitochondrial asparaginyl-tRNA.