A SIGNIFICANTLY IMPROVED SEMLIKI FOREST VIRUS EXPRESSION SYSTEM BASEDON TRANSLATION ENHANCER SEGMENTS FROM THE VIRAL CAPSID GENE

We recently described a system for heterologous gene expression in a v ariety of mammalian cell types that is based on an efficiently replica ting Semliki Forest virus (SFV) variant in which an RNA encoding a for eign protein replaces the RNA that normally encodes the viruses' struc tural polyprotein. Although expression levels are sufficiently high fo r many purposes, in general they are only 10% of the level of the poly protein in a wild type SFV infection. Here we show that the first 102 bases of the viral capsid gene function as a translational enhancer, a nd that SFV vectors incorporating this RNA increase heterologous prote in synthesis to the level of wild type polyprotein.