We have been studying the role that protein degradation plays in regulating cell growth control, through the study of the proteases which carry out ATP-dependent proteolysis in E. coli. The Lon protease degrades RcsA, a positive regulator of capsular polysaccharide synthesis, and SulA, a cell division inhibitor. We have demonstrated that RcsA interacts in the cell with another positive regulator, RcsB to promote efficient capsule synthesis. The Clp protease, a second major ATP-dependent protease, contains a large subunit, ClpA, with ATPase activity; this subunit has been well conserved in both other prokaryotic cells and eukaryotic cells. The smaller subunit, ClpP, contains the active site of the protease, and undergoes a self-processing reaction. The small subunit is also conserved in many cells. The structure and general organization of the Clp protease suggests that it has many similarities to the eukaryotic energy-dependent proteases which degrade ubiquitin-conjugated proteins. Alp, a third energy-dependent protease activity, which can substitute for Lon when overproduced, consists of a set of closely linked genes and a positive regulator. In another approach to the study of bacterial cell growth control, mutants which may be defective in partition of the bacterial chromosome have been selected, mapped and characterized.
