G3 BP 1 interacts directly with the FMDV IRES and negatively regulates translation

RNA –protein interactions play a pivotal role in the function of picornavirus internal ribosome entry site ( IRES ) elements. Here we analysed the impact of Ras GTP ase SH 3 domain binding protein 1 (G3 BP 1) in the IRES activity of foot‐and‐mouth disease virus ( FMDV ). We found that G3 BP 1 interacts directly with three distinct sequences of the IRES element using RNA electrophoretic mobility‐shift assays. Analysis of the interaction with domain 5 indicated that the G3 BP 1 binding‐site is placed at the single‐stranded region although it allows large sequence heterogeneity and the hairpin located upstream of this region enhances retarded complex formation. In addition, G3 BP 1 interacts directly with the polypyrimidine tract‐binding protein and the translation initiation factor 4B ( eIF 4B) through the C‐terminal region. Moreover, G3 BP 1 is cleaved during FMDV infection yielding two fragments, Ct‐G3 BP 1 and Nt‐G3 BP 1. Both fragments inhibit cap‐ and IRES ‐dependent translation , but the Ct‐G3 BP 1 fragment shows a stronger effect on IRES ‐dependent translation. Assembly of complexes with G3 BP 1 results in a significantly reduced local flexibility of the IRES element, consistent with the negative effect of this protein. Our results highlight the IRES ‐binding capacity of G3 BP 1 and illustrate its function as a translation inhibitor.