Intracellular behavior of rabies virus matrix protein (M) is determined by the viral glycoprotein (G)

To investigate the nature and intracellular behavior of the matrix (M) protein of an avirulent strain (HEP-Flury) of rabies virus, we cloned and sequenced the cDNA of the protein. Using expression vectors pZIP-NeoSV(X)1 and pCDM8, the cDNA was transfected to animal cells (BHK-21 and COS-7) with or without coexpression of viral glycoprotein (G), When M protein alone was expressed in the cells, it displayed homogeneous distribution in the whole cell including the nucleus. In contrast, coexpression with G protein resulted in the abolishment of nuclear distribution of M antigen, and both of the antigens displayed a colocalized distribution in the cell, especially at the cellular membrane as seen in the virus-infected cells, while the distribution of G antigen was not affected by coexpressed M antigen, Immunoprecipitation studies revealed that M protein was coprecipitated with G protein by anti-G antibody, and vice versa, although cross-linking with dithiobis (succinimidyl propionate) was necessary for coprecipitation because of their easier dissociation in the presence of sodium deoxycholate, These results suggest that M protein intimately associates with G protein, which may affect or regulate the behavior (e,g., intracellular localization) of M protein. Studies with deletion mutants of M protein indicate that an internal region around the amino acids from 115 to 151 is essential for the M protein to preserve its binding ability to G protein.