Purification, kinetic properties, and intracellular concentration of SpoIIE, an integral membrane protein that regulates sporulation in Bacillus subtilis

SpoIIE is a bifunctional protein which controls sigma(F) activation and for mation of the asymmetric septum in sporulating Bacillus subtilis. The spoII E gene of B. subtilis has now been overexpressed in Escherichia coli, and S poIIE has been purified by anion-exchange chromatography and affinity chrom atography. Kinetic studies showed that the rate of dephosphorylation of Spo IIAA-P by purified SpoIIE in vitro was 100 times greater, on a molar basis, than the rate of phosphorylation of SpoIIAA by SpoIIAB. The intracellular concentrations of SpoIIE and SpoIIAB were measured by quantitative immunobl otting between 0 and 4 h after the beginning of sporulation. The facts that these concentrations were very similar at hour 2 and that SpoIIE could be readily detected before asymmetric septation suggest that SpoIIE activity m ay be strongly regulated.