A cytotoxic ribonuclease targeting specific transfer RNA anticodons

The carboxyl-terminal domain of colicin E5 was shown to inhibit protein syn thesis of Escherichia coli. Its target, as revealed through in vivo and in vitro experiments, was not ribosomes as in the case of E3, but the transfer RNAs (tRNAs) for Tyr, His, Asn, and Asp, which contain a modified base, qu euine, at the wobble position of each anticodon. The E5 carboxyl-terminal d omain hydrolyzed these tRNAs just on the 3' side of this nucleotide. Tight correlation was observed between the toxicity of E5 and the cleavage of int racellular tRNAs of this group, implying that these tRNAs are the primary t argets of colicin E5.