Conditional synthesis of an aberrant glycoprotein mRNA by the internal deletion mutant of vesicular stomatitis virus.

The internal deletion mutant (DI-LT) derived from the heat-resistant strain of vesicular stomatitis virus synthesizes an aberrant polyadenylated mRNA (G*) containing a transcript of the partially deleted polymerase gene covalently linked to the 3' end of the glycoprotein message (R. C. Herman and R. A. Lazzarini, J. Virol. 40:78-86, 1981). The heat-resistant polymerase appears to play a role in the synthesis of the abnormal G* RNA. The synthesis of G* correlated directly with the presence of the heat-resistant L protein on the defective interfering particle template. Chimeric defective interfering particles produced by passaging DI-LT with a helper virus that encodes the wild-type vesicular stomatitis virus polymerase did not synthesize G*. The subsequent passage of the chimeric DI-LT with a heat-resistant helper virus restored the ability to synthesize the G* transcript. These results imply that the regulatory signals normally present at the vesicular stomatitis virus G/L intercistronic boundary may be preserved in DI-LT. These sequences are only conditionally functional because they are recognized correctly by the wild-type but not by the heat-resistant polymerase.