Imms bind specifically to cognate colicins in order to protect their host cells [1]. Imm-E5 is a specific inhibitor protein of colicin E5. It binds to E5 C-terminal ribonuclease domain (CRD) to prevent cell death. The binding mode of E5-CRD and Imm-E5 mimics that of mRNA and tRNA suggesting an evolutionary pathway from the RNA-RNA interaction through the RNA-protein interaction of tRNA/E5-CRD [1].

1: Structural basis for sequence-dependent recognition of colicin E5 tRNase by mimicking the mRNA-tRNA interaction. Yajima S, Inoue S, Ogawa T, Nonaka T, Ohsawa K, Masaki H; Nucleic Acids Res. 2006;34:6074-6082. PMID:17099236