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 initia tion 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. Ko walski, 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 t he nascent viral polyprotein and cleavage of eIF-4 gamma), we investig ated whether the FMDV L proteinase would also be able to stimulate tra nslation initiation, We found that purified recombinant FMDV Lb protei nase could stimulate in vitro translation driven from a rhinovirus or enterovirus IRES by 5- to 10-fold. In contrast, stimulation of transla tion 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 proteinas e indicated that stimulation of IRES-driven translation is mediated vi a proteolysis of some cellular component(s), Our studies also demonstr ated that the Lb proteinase is capable of stimulating initiation of tr anslation on an uncapped cellular message, Unexpectedly, and in contra st to the 2A proteinases, the Lb proteinase specifically cleaved the p roducts of the two reporter genes used in this study: Xenopus laevis c yclin B2 and influenza virus NS, Therefore, we also set out to investi gate 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 rep licase-related polylpeptides, In the latter case, the site(s) of cleav age was located within the N-terminal part of polypeptide 3D, Sequence comparisons revealed no significant primary sequence similarities bet ween the target proteins and the two sites already known to be recogni zed by the FMDV L proteinase,