Analysis of the stimulation of reporter gene expression by the sigma 3 protein of reovirus in co-transfected cells.

The stimulation of reporter gene expression following co-transfection with the S4 gene of mammalian reoviruses was analysed. The sigma 3 protein of type 3 reovirus gave a five- to eightfold increase in expression of chloramphenicol acetyltransferase and beta-galactosidase but this was found to be dependent upon the nature of the promoter being used to drive reporter gene expression. The sigma 3 protein of reovirus type 1 failed to stimulate reporter gene expression under any of the conditions used. Hybrid constructs between the S4 genes of reoviruses type 1 and 3 were used to map the stimulation characteristic to the carboxy-terminal third of the gene. Analysis of the level of sigma 3 protein accumulation in transfected cells showed that the reovirus type 3 protein accumulated to a much higher level than that of reovirus type 1. Using the hybrid gene constructs this higher level of protein accumulation was shown to co-segregate with the ability to stimulate reporter gene expression.