IDENTIFICATION OF REGIONS ON THE FUSION PROTEIN OF HUMAN PARAINFLUENZA VIRUS TYPE-2 WHICH ARE REQUIRED FOR HEMAGGLUTININ-NEURAMINIDASE PROTEINS TO PROMOTE CELL-FUSION

Using a plasmid expression system in HeLa cells, we have previously sh own that the fusion (F) protein of simian virus 41 (SV-41) induces cel l fusion when coexpressed with the haemagglutininneuraminidase (HN) pr otein of human parainfuenza virus type 2 (PIV-2), while the PIV-2 F pr otein does not induce cell fusion with the SV-41 HN protein, In the pr esent study, we found that the PIV-2 F protein induced extensive cell fusion with the HN protein of mumps virus (MuV), whereas the SV-41 F p rotein did not, Chimaeric analyses of the F proteins of PIV-2 and SV-4 1 identified two regions (designated M1 and M2) on the PIV-2 F protein , either of which was necessary for chimaeric F proteins to show fusog enic activity with the MuV HN protein, Subsequently, two additional re gions (P1 and P2) were identified on the PIV-2 F protein, both of whic h were necessary for chimaeric F proteins to prevent induction of cell fusion with the SV-41 HN protein, Consequently, it was proved that a given chimaeric F protein, harbouring regions P1 and P2 together with either of region M1 or M2, induced cell fusion specifically with HN pr oteins of PIV-2 and MuV, the same as the PIV-2 F protein, Region M2 wa s located at the membrane proximaI end of the PIV-2 F1 ectodomain, whi le regions P1, M1 and P2 clustered together in the middle of the ectod omain, These regions on the PIV-2 F protein may be involved in a putat ive functional interaction with HN proteins, which is considered to be a prerequisite for cell fusion.