Identification of a gene fragment which codes for the 364 amino-terminal amino acid residues of a SecA homologue from Bacillus subtilis: further evidence for the conservation of the protein export apparatus in gram-positive and gram-negative bacteria.

A DNA fragment that codes for the 364 amino-terminal amino acid residues of a putative Bacillus subtilis SecA homologue has been cloned using the Escherichia coli secA gene as a probe. The deduced amino acid sequence showed 58% identity to the amino-terminus of the E. coli SecA protein. A DNA fragment which codes for 275 amino-terminal amino acid residues of the B. subtilis SecA homologue was expressed in E. coli and the corresponding gene product was shown to be recognized by anti-E. coli SecA antibodies. This polypeptide, although only about 30% the size of the E. coli SecA protein, also restored growth of E. coli MM52 (secAts) at the non-permissive temperature and the translocation defect of proOmpA in this mutant was relieved to a substantial extent.