Regulation of viral transcription by the matrix protein of vesicular stomatitis virus probed by monoclonal antibodies and temperature-sensitive mutants.

The ability of the matrix (M) protein of wild-type vesicular stomatitis virus (VSV) to regulate viral transcription was studied with monoclonal antibodies and temperature-sensitive (ts) mutants in complementation group III, the M proteins of which are restricted in transcription inhibition. The marked inhibition of transcription by VSV ribonucleoprotein (RNP) cores complexed with M protein (RNP/M) was reversed by antibody to epitope 1. Antibodies to epitopes 2 and 3 not only failed to reverse the transcription-inhibitory activity of isolated M protein but actually increased M-protein inhibition of transcription in a reconstituted system. Monoclonal antibodies to epitopes 2 and 3 strongly bound to M proteins from all wild-type and ts-mutant virions, but monoclonal antibody to epitope 1 completely failed to bind to the M protein of ts023(III) even though it reacted strongly with M proteins of mutants tsG31(III) and tsG33(III). The M protein of a tsO23 revertant (R11) completely recovered its capacity to inhibit transcription and to bind monoclonal antibody to epitope 1, whereas the M proteins of three other revertants remained restricted in their capacity to inhibit transcription and to bind monoclonal antibody to epitope 1. These studies indicate that exposure of epitope 1 on the surface of M protein is essential for inhibiting transcription by VSV RNP cores.