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

To investigate the nature and intracellular behavior of the matrix (M) prot ein of an avirulent strain (HEP-Flury) of rabies virus, we cloned and seque nced the cDNA of the protein. Using expression vectors pZIP-NeoSV(X)1 and p CDM8, the cDNA was transfected to animal cells (BHK-21 and COS-7) with or w ithout coexpression of viral glycoprotein (G), When M protein alone was exp ressed in the cells, it displayed homogeneous distribution in the whole cel l including the nucleus. In contrast, coexpression with G protein resulted in the abolishment of nuclear distribution of M antigen, and both of the an tigens displayed a colocalized distribution in the cell, especially at the cellular membrane as seen in the virus-infected cells, while the distributi on of G antigen was not affected by coexpressed M antigen, Immunoprecipitat ion studies revealed that M protein was coprecipitated with G protein by an ti-G antibody, and vice versa, although cross-linking with dithiobis (succi nimidyl propionate) was necessary for coprecipitation because of their easi er dissociation in the presence of sodium deoxycholate, These results sugge st that M protein intimately associates with G protein, which may affect or regulate the behavior (e,g., intracellular localization) of M protein. Stu dies with deletion mutants of M protein indicate that an internal region ar ound the amino acids from 115 to 151 is essential for the M protein to pres erve its binding ability to G protein.