Direct evidence for a coupling between synthesis and export of PhoS in E. coli.

The accumulation of pre-PhoS under conditions of PhoS overproduction has been previously described. It is now demonstrated that during the induction of PhoS, a delay in the completion of polypeptide chain elongation can be detected. This delay is related to the extent of jamming of export sites by pre-PhoS or by other exported proteins. These results suggest that a component required for completion of pre-PhoS polypeptide becomes limiting, being titrated by the excess of nascent chains bearing signal peptides. This component thus probably acts at an early step in the export pathway.