This family consists of several bacterial proteins including ImpE (Swiss:Q93EC9) from Rhizobium leguminosarum. It has been suggested that the imp locus is involved in the secretion to the environment of proteins, including periplasmic RbsB protein, that cause blocking of infection specifically in pea plants [1]. The exact function of this family is unknown.

1: Infection-blocking genes of a symbiotic Rhizobium leguminosarum strain that are involved in temperature-dependent protein secretion. Bladergroen MR, Badelt K, Spaink HP; Mol Plant Microbe Interact 2003;16:53-64. PMID:12580282