Similarity of the FPI to other virulence gene clusters. Homologues of Francisella pathogenicity island proteins IglA and IglB are found on a conserved gene clusters known as IcmF associated homologous proteins (IAHP), which, in some cases encode a proposed type VI secretion system. In the FPI the IcmF motif appears at the C-terminus of PdpB. Downstream of the pdpB gene is an ORF designated "vgr" that encodes a protein with similarity the Vgr family, one of which is secreted by the proteins encoded by an IAHP cluster in Vibrio cholerae. Homologues of the Legionella dotU gene are often associated with IAHP clusters. A very weak similarity to dotU is seen in an ORF that is sixth downstream of pdpB.