Printed in Great Britain Cleavage of Virus-specified Polypeptides in Cells Infected with Semliki Forest Virus

Several new virus-specified polypeptides of high mol. wt. were detected in cells infected with Semliki Forest virus by use of pulse-chase methods in cells which had been either incubated at an elevated temperature in the presence of tosyl-L-phenylalanylchloromethane or tr ated with an inhibitor of glycoprotein synthesis, or an inhibitor ofproteolytic enzyme activity, or five amino acid analogues, or an inhibitor of protein synthesis. The new polypeptides had estimated mol. wt. of 165000, i27ooo and Io5ooo and were shown to be converted to lower mol. wt. polypeptides in pulse-chase experiments. These polypeptides, together with known non-structural polypeptides ofmol. wt. of 97 ooo, 78 ooo and 63 ooo are incorporated into a proposed cleavage mechanism for the synthesis of the virus structural proteins