Foot-and-mouth disease virus Lb proteinase can stimulate rhinovirus and enterovirus IRES-driven translation and cleave several proteins of cellular and viral origin.

Rhinovirus and enterovirus 2A proteinases stimulate translation initiation driven from the cognate internal ribosome entry segment (IRES) (S. J. Hambidge and P. Sarnow, Proc. Natl. Acad. Sci. USA 89:10272-10276, 1992; H.-D. Liebig, E. Ziegler, R. Yan, K. Hartmuth, H. Klump, H. Kowalski, D. Blaas, W. Sommergruber, L. Frasel, B. Lamphear, R. Rhoads, E. Kuechler, and T. Skern, Biochemistry 32:7581-7588, 1993). Given the functional similarities between the foot-and-mouth disease virus (FMDV) L proteinase and these 2A proteinases (autocatalytic excision from the nascent viral polyprotein and cleavage of eIF-4 gamma), we investigated whether the FMDV L proteinase would also be able to stimulate translation initiation. We found that purified recombinant FMDV Lb proteinase could stimulate in vitro translation driven from a rhinovirus or enterovirus IRES by 5- to 10-fold. In contrast, stimulation of translation initiation on a cardiovirus IRES by this proteinase was minimal, and stimulation of translation driven from the cognate FMDV IRES could not be evidenced. Studies using an inhibitor or a mutant Lb proteinase indicated that stimulation of IRES-driven translation is mediated via proteolysis of some cellular component(s). Our studies also demonstrated that the Lb proteinase is capable of stimulating initiation of translation on an uncapped cellular message. Unexpectedly, and in contrast to the 2A proteinases, the Lb proteinase specifically cleaved the products of the two reporter genes used in this study: Xenopus laevis cyclin B2 and influenza virus NS. Therefore, we also set out to investigate the requirements for substrate recognition by the Lb proteinase. Purified recombinant Lb proteinase recognized at least one mengovirus polypeptide and specifically cleaved human cyclin A and poliovirus replicase-related polypeptides. In the latter case, the site(s) of cleavage was located within the N-terminal part of polypeptide 3D. Sequence comparisons revealed no significant primary sequence similarities between the target proteins and the two sites already known to be recognized by the FMDV L proteinase.