Lack of effect of leader peptidase overproduction on the processing in vivo of exported proteins in Escherichia coli.

The kinetics of maturation of certain exported proteins were analysed in Escherichia coli strains that also concomitantly overproduce either a periplasmic protein or the leader peptidase. The results led to three conclusions. Overproduction of leader peptidase has no effect on the rate of maturation of at least two exported proteins, one periplasmic (TEM beta-lactamase), one outer membrane (PhoE); therefore, the quantity of leader peptidase is not rate-limiting for normal export. Overproduction of PhoS reduces the rate of maturation of two other periplasmic proteins (beta-lactamase and PhoA) and itself, presumably by competing for the rate-limiting component of the export apparatus. Overproduction of leader peptidase in a strain overproducing PhoS has no effect on the retarded maturation of PhoS. Therefore even in these conditions, leader peptidase is not rate limiting.