CHARACTERIZATION OF TRUNCATED FORMS OF THE KDPD PROTEIN, THE SENSOR KINASE OF THE K-TRANSLOCATING KDP SYSTEM OF ESCHERICHIA-COLI()

The expression of the kdpFABC operon, coding for the K+-translocating Kdp system, is controlled by the two regulatory proteins, KdpD and Kdp E, which belong to the group of sensor kinase/response regulator syste ms. This study describes the construction and analysis of KdpD sensor kinases, in which different deletions in the N-terminal part of the pr otein were introduced. Truncated KdpD proteins, in which the membrane- spanning segments were deleted, had lost their phosphorylation capacit y. Truncated KdpD proteins, in which the four membrane-spanning helice s were untouched, were still phosphorylated, and the phosphoryl group could be transferred to the response regulator KdpE in vitro. Furtherm ore, these truncated KdpD proteins cause dephosphorylation of KdpE(P), which is comparable with that of the wild-type protein. To investigat e the effect of the deletions on signal transduction in vivo the corre sponding kdp genes were transferred to the chromosome, Growth studies with the mutant strains are in accord with the data obtained from the in vitro studies. Furthermore, kdp expression was investigated using a KdpA-LacZ fusion. The data obtained support the notion that the exten t of hdp expression is modulated by the N-terminal part of KdpD.