Inactivation of cap-binding proteins accompanies the shut-off of host protein synthesis by poliovirus.

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Abstract
Infection of HeLa cells with poliovirus results in a rapid shut-off of host protein synthesis. It has been suggested that inactivation of a protein that binds to the cap structure of cellular mRNAs would explain the selective inhibition of host protein synthesis because the naturally uncapped poliovirus RNA can be translated by a cap-independent mechanism. To test directly for the presence of cap-binding proteins in poliovirus-infected and mock-infected cells, we analyzed initiation factor preparations for their ability to specifically crosslink to the 5' cap structure of oxidized reovirus mRNA. The data presented here show that the crosslinking ability of the different cap-binding proteins (24-, 28-, 32-, 50-, and 80-kilodalton polypeptides) is reduced in preparations from poliovirus-infected as compared to mock-infected cells. This reduction correlates with the inability of initiation factor preparations from infected cells to restore translation of capped mRNAs in extracts of poliovirus-infected cells. In addition, initiation factor preparations from poliovirus-infected cells have the ability to rapidly inactivate cap-binding proteins and can also impair the restoring activity of initiation factors from mock-infected cells.