Abstract
A cell-free system has been used to synthesize respiratory syncytial virus (RSV) RNA in vitro. Polyadenylated species representing all size classes of RSV mRNAs were labelled. Some of the labelled RNA was seen in a CsCl gradient at the density characteristic of negative-strand viral nucleocapsids. Experiments using a thiotriphos-phorylated nucleotide indicate that RNA chains are initiated de novo in the cell- free system.