Biogenesis of vaccina: Interrelationship between post-translational cleavage, virus assembly, and maturation

Abstract

Previously published investigations with inhibitors and temperature-sensitive ( ts) mutants revealed that post-translational cleavage (PTC) of virion core polypeptides is a necessary step for development of infectious, mature vaccinia virus. Present studies focused on the nature of the protease factor(s) required for vaccinia biogenesis. To ascertain whether the proteolytic factor(s) can move freely through the cytoplasm. PTC occurring during complementation between cleavage defective and DNA- ts mutants was compared with that evident following induced syncytiogenesis, involving cells singly inoculated with wild-type and cleavage-defective ts 1095 virus. Since PTC can occur during coinfection but not after cell-cell fusion, the protease factor is presumed to be on diffusible. This notion is supported by the incapacity of extracts from infected cells to bring about in vitro PTC. Data from temperature shift experiments with ts 1085 indicate that the factor(s) for proteolysis is probably a short-lived activity and affinity labeling suggests that if may be a virus-induced, nonvirion polypeptide p 12.5 in molecular weight, possessing the specificity of chymotrypsin for protease inhibitors TPCK and ZPCK. Evidence indicating that the factor has a brief half-life implies that it must be synthesized on a continuous basis to effect viral maturation. A model of vaccina self-assembly, which takes into account previous observations and current data, is proposed according to which induction of core enzymatic activities, internal differentiation, and aquisition of infectiousness are temporally coordinated, closely coupled phenomena requiring PTC.