A number of bacterial proteins, some of which are involved in a general secretion pathway (GSP) for the export of proteins (also called the type II pathway) [1,2,3,4,5], have been found to be evolutionary related. These proteins are listed below:

• The 'D' protein from the GSP operon of: Aeromonas (gene exeD); Erwinia (gene outD); Escherichia coli (gene yheF), Klebsiella pneumoniae (gene pulD); Pseudomonas aeruginosa (gene xcpQ); Vibrio cholerae (gene epsD) and Xanthomonas campestris (gene xpsD).
• comE from Haemophilus influenzae, involved in competence (DNA uptake).
• pilQ from Pseudomonas aeruginosa, which is essential for the formation of the pili.
• hofQ (hopQ) from Escherichia coli.
• hrpH from Pseudomonas syringae, which is involved in the secretion of a proteinaceous elicitor of the hypersensitivity response in plants.
• hrpA1 from Xanthomonas campestris pv. vesicatoria, which is also involved in the hypersensitivity response.
• mxiD from Shigella flexneri which is involved in the secretion of the Ipa invasins which are necessary for penetration of intestinal epithelial cells.
• omc from Neisseria gonorrhoeae.
• yssC from Yersinia enterocolitica virulence plasmid pYV, which seems to be required for the export of the Yop virulence proteins.
• The gpIV protein from filamentous phages such as f1, ike, or m13. GpIV is said to be involved in phage assembly and morphogenesis.

These proteins all seem to start with a signal sequence and are thought to be integral proteins in the outer membrane. As a signature pattern we selected a conserved region in the C-terminal section of these proteins.