CARBON SOURCE-DEPENDENT SYNTHESIS OF SECB, A CYTOSOLIC CHAPERONE INVOLVED IN PROTEIN TRANSLOCATION ACROSS ESCHERICHIA-COLI MEMBRANES

SecB is a cytosolic chaperone involved in protein translocation across cytoplasmic membranes in Escherichia coli. It has been shown to be re quired for efficient translocation of a subset of precursor proteins b ut is not essential for cell viability. This study investigated whethe r synthesis of SecB is growth rate dependent. Interestingly, the total amount of SecB synthesized in the cells was relatively small, Moreove r, the levels of SecB were found to be carbon source dependent since m ore SecB was produced in cells grown in glycerol media than in cells g rown in glucose media, regardless of the growth rate. This is in contr ast to the other Sec proteins, whose synthesis is growth rate dependen t and not related to glucose as a carbon source, In addition, cyclic A MP (cAMP) partially relieves the lower levels of SecB observed in gluc ose medium, a compensatory effect that depends on the presence of both cya and crp gene products. Thus, the glucose-dependent synthesis of S ecB may be related to the cAMP-cAMP receptor protein complex-mediated activation.