INDEPENDENT GENES FOR 2 THREONYL-TRANSFER RNA-SYNTHETASES IN BACILLUS-SUBTILIS

With the exception of Escherichia coli lysyl-tRNA synthetase, the genes coding for the different aminoacyl-tRNA synthetases in procaryotes are always unique. Here we report on the occurrence and cloning of two genes (thrSv and thrS2), both encoding functional threonyl-tRNA synthetase in Bacillus subtilis. The two proteins share only 51.5% identical residues, which makes them almost as distinct from each other as each is from E. coli treonyl-tRNA synthetase (42 and 47%). Both proteins complement an E. coli thrS mutant and effectively charge E. coli threonyl tRNA in vitro. Their genes have been mapped to 250° (thrSv) and 344° (thrS2) on the B. subtilis chromosome. The regulatory regions of both genes are quite complex and show structural similarities. During vegetative growth, only the thrSv gene is expressed.