Co-transcription of Rhizobium meliloti lysyl-tRNA synthetase and glutamyl-tRNA synthetase genes.

An open reading frame encoding a putative polypeptide very similar to several lysyl-tRNA synthetases was found 10 nucleotides downstream of Rhizobium meliloti gltX encoding glutamyl-tRNA synthetase. Expression of this gene complemented a mutation in lysS of Escherichia coli and led to the overexpression of a polypeptide of the expected mass (62 kDa), thus confirming that it encodes R. meliloti lysyl-tRNA synthetase. Reverse transcription/polymerase chain reaction was used to demonstrate that this lysS gene is co-transcribed with gltX in R. meliloti. This is the first reported case of two immediately adjacent and co-transcribed genes encoding aminoacyl-tRNA synthetases.