Initiation of protein synthesis in cell-free extracts of Tetrahymena pyriformis.

Saturating concentrations of the initiation-specific inhibitors poly(I) and T-2 toxin inhibit protein synthesis by over 35% and cause ribosome 'run-off' from the polyribosomes. The elongation-specific inhibitor cycloheximide totally prevents protein synthesis and 'freezes' the ribosomes in the pattern of unincubated controls. These results prove that our Tetrahymena extracts are capable of protein-synthesis initiation, a conclusion which is confirmed by a 30% inhibition of synthesis by the mRNA cap analogue, 7-methylguanosine 5'-monophosphate.