Revised translation start site for secM defines an atypical signal peptidethat regulates Escherichia coli secA expression

The secretion-responsive regulation of Escherichia coli secA occurs by coup ling its translation to the translation and secretion of an upstream regula tor, secM (formerly geneX). We revise the translational start site for secM , defining a new signal peptide sequence with an extended amino-terminal re gion. Mutational studies indicate that certain atypical amino acyl residues within this extended region are critical for proper secA regulation.