Compositions and methods are disclosed for expressing heterologous coding sequences in host cells. The compositions include infectious Sindbis virus RNA molecules containing at least one heterologous coding sequence inserted within the structural region of the Sindbis virus genome. RNA molecules consisting essentially of a Sindbis virus junction region are also provided. Methods utilizing the novel compositions of the present invention to express heterologous coding sequences in transformed host cells are provided. Methods for producing infectious Sindbis virus particles containing infectious Sindbis virus RNA molecules comprising at least one heterologous coding sequence are provided.This invention was made with government support under grant numbers AI24134, AI11377 and AG05681 awarded by the National Institutes of Health. The government has certain rights in the invention.