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GcvA is a member of the LysR family of transcriptional regulators that mediates the expression of the glycine cleavage (GCV) operon (gcvTHP) in response to glycine in Escherichia coli. In our previous work, 90 putative regulator genes of the LysR family in Sinorhizobium meliloti were mutagenized to determine their phenotype. In the present study, we found that the S. meliloti genome had two gcvA genes, gcvA1 and gcvA2. Both gcvA1 and gcvA2 were required for full activation of the gcvTHP operon in the presence of exogenous glycine. The gcvA1-mediated activation of gcvTHP operon was gly- cine-inducible, while gcvA2-mediated activation was not. We speculate that the regulatory mechanism for gcvTHP expression in S. meliloti differed from E. coli. Evolutionary analysis showed that GcvA were distributed in many genera of Proteobacteria and the distances between GcvA1 and GcvA2 in S. meliloti and GcvA in E. coli were large, which may explain the different regulatory mechanisms for gcvTHP expression. These findings could provide new clues to the role of the LysR gene family.
GcvA is a member of the LysR family of transcriptional regulators that mediates the expression of the glycine cleavage (GCV) operon (gcvTHP) in response to glycine in Escherichia coli. In our previous work, 90 putative regulator genes of the LysR family in Sinorhizobium meliloti were the mutagenized to determine their phenotype. In the present study, we found that the S. meliloti genome had two gcvA genes, gcvA1 and gcvA2. Both gcvA1 and gcvA2 were required for full activation of the gcvTHP operon in the presence of exogenous glycine. The gcvA1-mediated activation of gcvTHP operon was gly-cine-inducible, while gcvA2-mediated activation was not. We speculate that the regulatory mechanism for gcvTHP expression in S. meliloti differed from E. coli. Evolutionary analysis showed that GcvA were distributed in many genera of Proteobacteria and the distances between GcvA1 and GcvA2 in S. meliloti and GcvA in E. coli were large, which may explain the different regulatory mechanisms for gcvTHP expr ession. These findings could provide new clues to the role of the LysR gene family.