Effect of MetR protein on the in vitro expression of the metE, metH and metR genes.
N. Brot, M. Maxon, X-Y. Cai, B. Redfield, K. Fujita, G. Stauffer, I.G. Old, R. E. Glass & H. Weissbach.
Genetic studies have provided evidence for the existence of a new Met regulatory locus (metR) that is involved in the expression of the metE (non vitamin B12 transmethylase) and metH (B12 transmethylase) genes in Salmonella typjimurium and Escherichia coli (Urbanowski et al., J. Bact. 169, 1391-1397, 1987). In both organisms, the metR and metE genes are closely linked but transcribed in opposite directions. The 238 base intergenic region between the metE and metR genes in E. coli has been sequenced and shown to contain 7 met boxes (Belfaiza et al. Proc Natl Acad Sci USA 83, 867-871, 1986). The metR gene has been cloned into a high expresion vector and the MetR protein partially purified (~50% pure) from these cells. The purified protein markedly stimulates the expression of the metE and metH genes in an in vitro S-30 protein synthesis system using plasmids that contain these genes as templates. In addition, the metR gene appears to be autoregulated by the MetR protein. The MetJ protein and S-adenosylmethionine, which are known to repress the expression of other genes in the met regulon, inhibit the synthesis of MetR and MetE proteins in vitro while the synthesis of the MetH protein is unaffected.
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