Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Sun, 30 Dec 2018 01:51:27 J. gen. Virol. (I977), 35, 28x-297 281 Printed in Great Britain Biochemical Mapping of the Foot-and-Mouth Disease Virus Genome By D. V. SANGAR, D. N. BLACK, D. J. ROWLANDS AND F. BROWN Animal Virus Research Institute, Pirbright, Surrey (Accepted 7 December ~ 976) SUMMARY Four primary cleavage products, mol. wt. lO3× IOO, 88, 56 and 52 (Pioo, P88, P56 and P52 respectively) are present in BHK 21 cells infected with foot-and- mouth disease virus (FMDV). However, no precursor polyprotein equal to the sum of their mol. wt. was detected, even when amino acid analogues and proteo- lytic enzyme inhibitors were used. Three of the primary products were shown to cleave to smaller polypeptides, including the capsid polypeptides of the virus. Polypeptide P88, which was shown to be the precursor of the capsid polypeptides, is translated from the gene located at the 5'-end of the genome. The order of the structural polypeptides, determined by the use of emetine, is VP,, VP~, VPs, VPv The order of the remaining primary cleavage products is P52, P56 and PIo~. P56 is a stable product, identical with the virus infection associated (VIA) antigen found in virus harvests. The function of the other two products P52 and PIoo is not known. FMDV thus differs from other picornaviruses in that there is an extra primary cleavage product, apparently resulting from translation of more of the virus genome. INTRODUCTION The biosynthesis of picornavirus proteins proceeds by uninterrupted translation of the genome and the product is processed by a series of proteolytic cleavages (Holland & Kiehn, 1968; Jacobson & Baltimore, I968; Summers & Maizel, I968 ). The first series of cleavages occurs on the nascent protein so that the complete polyprotein is usually found only in abnormal conditions such as when the virus is grown in the presence of amino acid analogues (Jacobson, Asso & Baltimore, I97O) or when appropriate ts mutants are grown at a restrictive temperature (Garfinkle & Tershak, I971). However, traces of the complete polyprotein have been observed after giving a short pulse of radioactivity to cells infected with Coxsackie BI virus in normal culture conditions (Kiehn & Holland, 197o). The primary cleavages appear to be mediated by host enzyme(s) while the subsequent cleavages probably involve virus specified enzymes (Korant, 1972 ). Three primary cleavage products have been described in several picornavirus infected cell systems (Taber, Rekosh & Baltimore, I97I ; Butterworth & Rueckert, I972a). A feature of this mechanism is that there is a single ribosome binding site located near the 5'-end of the virus RNA. This has facilitated biochemical mapping of the gene products, either by pulsing with radioactivity at intervals after the inhibition of ribosome initiation with pactamycin (Summers & Maizel, I97I ; Taber et al. I97I; Butterworth & Rueckert, 19 VIR 35