NH2-terminal acidic region of the phosphoprotein of vesicular stomatitis virus can be functionally replaced by tubulin.

The phosphoprotein (NS) of vesicular stomatitis virus is an indispensable subunit of the virion-associated RNA polymerase (L). NS consists of a highly acidic NH2-terminal domain and a basic COOH-terminal domain. Unlike the latter, the amino acid sequences of the NH2-terminal regions are highly dissimilar among different viral serotypes, although they share structural similarities. We have cloned an NS gene into the SP6 transcription vector and replaced the 5'-terminal 80% by a full-length gene for beta-tubulin, which contains an acidic COOH-terminal domain. Here we present evidence that the chimeric tubulin-NS protein is biologically active and that the acidic region in tubulin directly affects the transcription reaction. These observations indicate that NS probably functions as an activator protein in which the acidic domain stimulates transcription of the viral genes by interacting with the RNA polymerase as observed for eukaryotic cellular transcription activators.