Identification of the catalytic residues of sequence-specific and histidine-free ribonuclease colicin E5.

Colicin E5 cleaves tRNAs for Tyr, His, Asn and Asp in their anticodons to abolish protein synthesis in Escherichia coli. We previously showed how its C-terminal RNase domain, E5-CRD, recognizes the anticodon bases but the catalytic mechanism remained to be elucidated. Although the reaction products with 5'-OH and 2',3'-cyclic phosphate ends suggested a similar mechanism to those of RNases A and T1, E5-CRD does not have the His residues necessary as a catalyst in usual RNases.