ZF-RNase-3 is one of the RNases from zebrafish (Danio rerio) with special (. noncatalytic) properties. These include angiogenic and bactericidal activities. Given the interest of fish RNases as host-defense effectors, we studied the mechanism of the bactericidal action of ZF-RNase-3 onEscheri-chia coli as a model Gram-negative bacterium.