CLEAVAGE OF INCOMING SEMLIKI-FOREST-VIRUS CAPSID PROTEIN WITHIN THE ENDOCYTOTIC PATHWAY - A FEATURE COMMON TO BOTH INVERTEBRATE AND MAMMALIAN-CELLS

During the initial stages of Semliki Forest virus (SFV) infection in m ammalian (baby hamster kidney, BHK) cells, the cleavage of SFV capsid protein could be detected. Analysis of subcellular fractions from SFV- infected BHK cells showed that (a) cleavage of the capsid protein occu rred within a prelysosomal compartment of the endocytotic pathway, and (b) following release of the nucleocapsid into the cytoplasm, a 17.5 kD capsid protein fragment could be detected in the subcellular fracti on which contained ribosomes. We have previously reported the cleavage of incoming SFV capsid protein in mosquito cells, too. Thus, the prot eolytic cleavage of incoming SFV capsid protein is a feature which is common to both invertebrate and mammalian cells. These data further su pport our hypothesis that the cleavage of incoming capsid protein migh t provide the conformational change which primes the SFV nucleocapsid for uncoating.