VACCINIA VIRUS PROTEIN-SYNTHESIS HAS A LOW REQUIREMENT FOR THE INTACTTRANSLATION INITIATION-FACTOR EIF4F, THE CAP-BINDING COMPLEX, WITHIN INFECTED-CELLS

The role of the cap-binding complex, eIF4F, in the translation of vacc inia virus mRNAs has been analyzed within infected cells. Plasmid DNAs , which express dicistronic mRNAs containing: a picornavirus internal ribosome entry site, produced within vaccinia virus-infected cells bot h beta-glucuronidase and a cell surface-targeted single-chain antibody (sFv), Cells expressing sFv were selected from nonexpressing cells, e nabling analysis of protein synthesis specifically within the transfec ted cells, Coexpression of poliovirus 2A or foot-and-mouth disease vir us Lb proteases, which cleaved translation initiation factor eIF4G, gr eatly inhibited cap-dependent protein (beta-glucuronidase) synthesis. Under these conditions, internal ribosome entry site-directed expressi on of sFv continued and cell selection was maintained. Furthermore, va ccinia virus protein synthesis persisted in the selected cells contain ing cleaved eIF4G. Thus, late vaccinia virus protein synthesis has a l ow requirement for the intact cap-binding complex eIF4F. This may be a ttributed to the short unstructured 5' noncoding regions of the vaccin ia virus mRNAs, possibly aided by the presence of poly(A) at both 5' a nd 3' termini.