Regulation of activity of a transcriptional anti-terminator in E. coli by phosphorylation in vivo.

Expression of the bgl operon of Escherichia coli is regulated in vitro by phosphorylation and dephosphorylation of a positive regulatory protein, BglG, which functions in its nonphosphorylated state as a transcriptional antiterminator. The degree of phosphorylation of BglG in vivo was shown to be dependent on the cellular levels of BglF protein, which is both the BglG kinase and phosphatase. The degree of phosphorylation of BglG also depended on the presence or absence of a beta-glucoside, the inducer of operon expression. Addition of inducer to cells in growth medium resulted in rapid dephosphorylation of phosphorylated BglG. The bgl operon is thus regulated by a sensory system that modulates gene expression by protein phosphorylation and dephosphorylation in response to the external levels of inducer.