REGULATION OF ESCHERICHIA-COLI SECA BY CELLULAR PROTEIN SECRETION PROFICIENCY REQUIRES AN INTACT GENE-X SIGNAL SEQUENCE AND AN ACTIVE TRANSLOCON

secA is translationally regulated by the protein secretion proficiency state of the Escherichia coli cell. This regulation was explored by m aking signal sequence mutations in the gene upstream of secA, gene X, which promotes secA translational coupling. Gene X signal sequence mut ants were constitutive for secA expression, while prlA alleles partial ly restored secA regulation. These results show that interaction of th e pre-gene X protein with the translocon is required for proper secA r egulation. Furthermore, gene X signal sequence mutations disrupted sec A regulation only in the cis configuration. We propose that nascent pr e-gene X protein interacts with the translocon during its secretion to constitute the secretion sensor.