Accumulation of prolipoprotein in Escherichia coli mutants defective in protein secretion.

The export of lipoprotein has been found to be affected in both secA and secY mutants of Escherichia coli which are defective in the secretion of a number of outer membrane and periplasmic proteins. The kinetics of accumulation of prolipoprotein upon a temperature shift to 42 degrees C is indistinguishable from that of pre-OmpA protein accumulation in the secA mutant. In both secA and secY mutants, the accumulated prolipoprotein is unmodified with glyceride and localized in the cytoplasmic membrane. We conclude from these results that the early steps in protein export are common to prolipoprotein and non-lipoprotein precursors. The pathways for the export of these two groups of precursor proteins diverge with regard to the modification and processing reactions which are late events in the export process.