Relaxed tRNA specificity of the Staphylococcus aureus aspartyl-tRNA synthetase enables RNA-dependent asparagine biosynthesis

The human pathogen Staphylococcus aureus is an asparagine prototroph despite its genome not encoding an asparagine synthetase. S. aureus does use an asparaginyl-tRNA synthetase (AsnRS) to directly ligate asparagine to tRNAAsn. The S. aureus genome also codes for one aspartyl-tRNA synthetase (AspRS). Here we demonstrate the lone S. aureus aspartyl-tRNA synthetase has relaxed tRNA specificity and can be used with the amidotransferase GatCAB to synthesize asparagine on tRNAAsn. S. aureus thus encodes both the direct and indirect routes for Asn-tRNAAsn formation while encoding only one aspartyl-tRNA synthetase. The presence of the indirect pathway explains how S. aureus synthesizes asparagine without either asparagine synthetase.