Regulation of translation by ribosome shunting through phosphotyrosine-dependent coupling of adenovirus protein 100k to viral mRNAs.

Adenovirus simultaneously inhibits cap-dependent host cell mRNA translation while promoting the translation of its late viral mRNAs during infection. Studies previously demonstrated that tyrosine kinase activity plays a central role in the control of late adenovirus protein synthesis. The tyrosine kinase inhibitor genistein decreases late viral mRNA translation and prevents viral inhibition of cellular protein synthesis. Adenovirus protein 100k blocks cellular mRNA translation by disrupting the cap-initiation complex and promotes viral mRNA translation through an alternate mechanism known as ribosome shunting. 100k protein interaction with initiation factor eIF4G and the viral 5' noncoding region on viral late mRNAs, known as the tripartite leader, are both essential for ribosome shunting. We show that adenovirus protein 100k promotes ribosome shunting in a tyrosine phosphorylation-dependent manner. The primary sites of phosphorylated tyrosine on protein 100k were mapped and mutated, and two key sites are shown to be essential for protein 100k to promote ribosome shunting. Mutation of the two tyrosine phosphorylation sites in 100k protein does not impair interaction with initiation factor 4G, but it severely reduces association of 100k with tripartite leader mRNAs. 100k protein therefore promotes ribosome shunting and selective translation of viral mRNAs by binding specifically to the adenovirus tripartite leader in a phosphotyrosine-dependent manner.