All five cold-shock domains of unr (upstream of N-ras) are required for stimulation of human rhinovirus RNA translation

Efficient translation of human rhinovirus-2 (HRV-2) RNA from its internal ribosome entry site (IRES) depends on the presence of cellular trans-acting factors upstream of N-ras (unr) and polypyrimidine-tract-binding protein. unr contains five cold-shock domains (CSDs)and is predicted to act as an RNA chaperone, allowing the HRV-2 IRES to attain the correct conformation for ribosome binding. To investigate the role of each of the CSDs in IRES-dependent translation, five unr mutants, each harbouring a point mutation in a different CSD, were generated. All five mutants were severely impaired in their ability to bind to the IRES and to stimulate translation from it. This showed that the ability of unr to function as an activator of HRV-2 RNA translation requires the RNA-binding activity of all five CSDs.