Activity of Colicin E3-Treated Ribosomes

Colicin E3 (called E3 here) is shown to act on polysomal ribosomes as well as on free ribosomes. This treatment severely inhibits subsequent chain elonga- tion, both on preformed polysomes completing their na- scent chains and on ribosomes translating poly(U). Ele- vated Mg++ concentration relieves this inhibition. How- ever, elevated Mg++ concentration does not relieve the inhibition of ribosomes initiating on natural messenger; hence damage by E3 appears to have an additional, specific effect on some stage in initiation. The effect of damage by E3 resembles that of streptomy- cin in several respects. This similarity suggests that the two agents may act on closely related sites on the ribo- some.