We have been studying the role that protein degradation plays in regulating cell growth control, through the study of mutants defective in ATP-dependent and independent protein turnover. E. coli lon mutants are defective in cell division regulation after DNA damage, and overproduce capsular polysaccharide. We have previously shown that an unstable positive regulator of capsule synthesis, RcsA, is stabilized in lon mutants. The rcsA function seems to be common to a number of gram-negative prokaryotes, suggesting a common mechanism for regulating different capsules in these strains. RcsC, a negative regulator of capsule synthesis, is a membrane protein which may act as a sensor for environmental signals controlling capsule synthesis. The gene for the ATP- binding subunit of a new two component ATP-dependent protease has been isolated, and chromosomal mutations in the gene, called clpA, have been generated. While cells devoid of clpA are healthy, the Clp protease seems to act as a back-up to lon in degrading abnormal proteins. A third protease function has been identified, and the gene responsible has been mapped to 56 minutes on the E. coli chromosome.
