SIGNAL-TRANSDUCTION IN THE RHIZOBIUM-MELILOTI DICARBOXYLIC-ACID TRANSPORT-SYSTEM

The gene products of the Rhizobium meliloti dctB and dctD genes, which control the expression of the C-4-dicarboxylic acid transporter DctA, were overproduced in Escherichia coli and purified. The purified sens or protein, DctB, was shown to have autophosphorylation activity in vi tro and could subsequently phosphorylate the transcriptional activator , DctD. The presence of C-4-dicarboxylic acids did not affect either r eaction. In vitro experiments aimed at investigating 'crosstalk' betwe en cognate components demonstrated that the phospho-transfer activity was specific between DctB and DctD. Studies on truncated versions of t he DctB protein in vitro revealed that the cytoplasmic domain of DctB had strong autophosphorylation activity. Data from gel retardation exp eriments demonstrated that once the activator protein, DctD, was phosp horylated it had increased affinity for binding to the dctA promoter D NA.