Specific interactions of vesicular stomatitis virus L and NS proteins with heterologous genome ribonucleoprotein template lead to mRNA synthesis in vitro.

Two dissociable proteins, L and NS, and N-RNA template were purified from two serologically distinct vesicular stomatitis viruses, Indiana [VSV(IND)] and New Jersey [VSV(NJ)]. Requirements for RNA synthesis in heterologous reconstitution reactions in vitro were studied. The L and NS proteins of VSV(NJ) failed to synthesize full-length leader RNA and mRNAs in vitro when reconstituted with N-RNA(IND) template. However, when purified homologous NS(IND) was added to the reaction mixture, mRNA synthesis ensued. The requirements for transcription of N-RNA(NJ) template were different from those for N-RNA(IND). For RNA synthesis, transcription specifically required L(NJ), but the NS(NJ) and NS(IND) proteins were interchangeable. This suggests that there are specific domains on the L(NJ) protein, at which NS proteins of both serotypes may interact to form an active RNA polymerase complex, whereas L(IND) lacked such domains for interaction with NS(NJ). The function of the L protein appeared primarily to initiate RNA chains, and the NS protein was required for chain elongation. The results of these in vitro complementation experiments are discussed in light of previous in vivo complementation studies.