Transcriptional regulation of the methionine and cysteine transport and metabolism in streptococci.

In streptococci, unlike other Firmicutes, methionine biosynthesis is controlled by protein transcription factors, rather than regulatory RNAs. It was observed that most available streptococcal genomes contain orthologs of two transcriptional regulators of the LysR family: MtaR/MetR and CmbR/FhuR. Comparative genomics techniques were applied to identify two binding motifs occurring upstream of genes involved in metabolism and transport of methionine and cysteine and satisfying the LysR family requirements. The distribution of candidate binding sites allowed to set the correspondence between motifs and regulators (TATAGTTTnAAACTATA for MtaR/MetR and TGATA-N(9)-TATCA-N(2-4)-TGATA for CmbR). Two amino acid transporters were predicted to belong to the cysteine (CmbR) regulon. At least two cases of potential regulator change were observed for orthologous genes of the methionine and cysteine pathway.