In E. coli the two proteins AntA and AntB have 62% amino acid identities near their N termini. AntA appears to be encoded by a truncated and divergent copy of AntB. The two proteins are homologous to putative antirepressors found in numerous bacteriophages, such as the hypothetical antirepressor protein encoded by the gene LO142 of the bacteriophage 933W [1].

1: Activation of prophage eib genes for immunoglobulin-binding proteins by genes from the IbrAB genetic island of Escherichia coli ECOR-9. Sandt CH, Hopper JE, Hill CW; J Bacteriol 2002;184:3640-3648. PMID:12057959