in vitro yeast reconstituted translation system reveals function of eIF5A for synthesis of long polypeptide.

We have recently developed an in vitro yeast reconstituted translation system, which is capable of synthesizing long polypeptides. Utilizing the system, we examined the role of eIF5A and its hypusine-modification in translating polyproline sequence within long ORFs. We found that polyproline-motif inserted at the internal position of the protein arrests translation exclusively at low Mg2+ concentrations, and peptidylpolyproline-tRNA intrinsically destabilizes 80S ribosomes. We demonstrate that unmodified eIF5A essentially resolves such ribosome-stalling, however, the hypusine-modification drastically stimulates ability of eIF5A to rescue polyproline-mediated ribosome stalling, and is particularly important for the efficient translation of the N-terminal or long internal polyproline-motifs.