Molecular cloning and nucleotide sequence of the gene for Escherichia coli leucyl-tRNA synthetase

The gene for Escherichia coli leucyl-tRNA synthetase leuS has been cloned by complementation of a leuS temperature sensitive mutant KL231 with an E.coli gene bank DNA. The resulting clones overexpress leucyl-tRNA synthetase (LeuRS) by a factor greater than 50. The DNA sequence of the complete coding regions was determined. The derived N-terminal protein sequence of LeuRS was confirmed by independent protein sequencing of the first 8 aminoacids. Sequence comparison of the LeuRS sequence with all aminoacyl-tRNA synthetase sequences available reveal a significant homology with the valyl-, isoleucyl- and methionyl-enzyme indicating that the genes of these enzymes could have derived from a common ancestor. Sequence comparison with the gene product of the yeast nuclear NAM2-1 suppressor allele curing mitochondrial RNA maturation deficiency reveals about 30% homology.