Translation of Semliki‐Forest‐Virus 42‐S RNA in a Mouse Cell‐Free System to give Virus‐Coat Proteins

Semliki‐Forest‐virus 42‐S virion RNA is translated in a mouse ascites cell‐free system. One of the major polypeptides made in vitro has been identified as Semliki‐Forest‐virus capsid protein by co‐electrophoresis on dodecylsulfate–polyacrylamide gels and by tryptic peptide analysis on paper. Another major product of the cell‐free system has been characterised as envelope protein by peptide analysis but it does not co‐electrophorese on gels with envelope proteins from purified virions. It is possible that the nascent, non‐glycosylated polypeptide is partially degraded by proleolytic enzymes present in the cell‐free extract, or alternatively that fragments of envelope protein are produced by premature termination on the viral RNA. Several other polypeptides are synthesised in the cell‐free system in variable amounts but these have not been identified. The genetic content and the mechanism of translation of Semliki‐Forest‐virus 42‐S RNA are discussed.