THE KDP SYSTEM OF CLOSTRIDIUM-ACETOBUTYLICUM - CLONING, SEQUENCING, AND TRANSCRIPTIONAL REGULATION IN RESPONSE TO POTASSIUM CONCENTRATION

The complete sequence of the kdp gene region of Clostridium acetobutyl icum has been determined. This part of the chromosome comprises two sm all open reading frames (orfZ and orfY), putatively encoding hydrophob ic peptides, and the genes kdpA, kdpB, kdpC, and kdyX, followed by an operon encoding a pair of sensor effector regulatory proteins (KdpD an d KdpE). Except for orfZ, orfY, and kdpX, all genes showed significant homology to the kdp genes of Escherichia coli, encoding a high-affini ty potassium transport ATPase and its regulators. The complete genome sequence of Synechocystis sp. strain PCC 6803 and a recently published part of the Mycobacterium tuberculosis genome indicate the existence of a kdp system in these organisms as well, but all three systems comp rise neither a second orf upstream of kdpA nor an additional kdpX gene . Expression of the clostridial kdp genes, including the unique kdpX g ene, was found to be inducible by low potassium concentrations. A tran scription start point could be mapped upstream of orfZ. A promoter ups tream of kdpD was active only under noninducing conditions. Lowering t he potassium content of the medium led to formation of a common transc ript (orfZYkdpABCXDE), with a putative internal RNase E recognition si te, which could be responsible for the instability of the common trans cript. Except for the two small peptides, all gene products could be d etected in in vitro transcription-translation experiments.