Abstract
Two distinct routes for attaching asparagine (Asn) to its cognate transfer RNA (tRNAAsn), an essential step in protein synthesis, are known. The one-step, direct pathway uses an asparaginyl-tRNA synthetase (AsnRS) to aminoacylate Asn to tRNAAsn. In organisms lacking AsnRS, a two-step pathway is used. First a non-discriminating aspartyl-tRNA synthetase (ND-AspRS) attaches aspartate (Asp) to tRNAAsn. The Asp is then amidated to Asn by GatCAB. Despite Bacillus subtilis using AsnRS for Asn-tRNAAsn production and GatCAB for Gln-tRNAGln formation, we predicted the lone B. subtilis AspRS is non-discriminating to enable the organism to also use the two-step pathway for Asn-tRNAAsn formation. Our in vitro and in vivo results are consistent with the AspRS using tRNAAsn as a substrate as the first step in tRNA-dependent Asn biosynthesis. B. subtilis encoding a tRNA-dependent route for Asn production would explain why the organism is able to grow in the absence Asn when all three of its glutamine-dependent Asn synthetases are knocked out. This work was supported by Skidmore College and the National Science Foundation (MCB-1244326)
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