A protein with sequence identity to Skp (FirA) supports protein translocation into plasma membrane vesicles of Escherichia coli.

We have purified to homogeneity a 15 kDa-protein from a ribosomal salt extract of Escherichia coli that compensates in vitro a defect of SecA but not of SecB. Removal of this protein from a cell-free transcription/translation system impairs translocation into plasma membrane vesicles of the precursors of LamB and to a lesser degree also of OmpA. These results suggest a role of the 15 kDa-protein in bacterial protein export. The NH2-terminal 35 amino acids were found to be identical to those of the skp (firA) gene product, to which several putative functions have previously been attributed.