Colicin is a protein produced by bacteria with Col plasmids. Its function is to attack E. coli through actions on its inner membrane ion channels or through ribonuclease or deoxyribonuclease actions. The C terminal domain is the ribonuclease domain. It specifically cleaves tRNA anticodons which recognise codons in the form NAY (N:any nucleotide, A:adenosine, Y:pyrimidine) which corresponds to Tyrosine, Histidine, Asparagine and Aspartic Acid. E5-CRD can be referred to as an RNA restriction enzyme that specifically recognizes and cleaves single-stranded GU sequences. [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