QUANTITATIVE MEASUREMENT OF PARAMYXOVIRUS FUSION - DIFFERENCES IN REQUIREMENTS OF GLYCOPROTEINS BETWEEN SIMIAN-VIRUS-5 AND HUMAN PARAINFLUENZA-VIRUS-3 OR NEWCASTLE-DISEASE VIRUS

To compare the requirements for paramyxovirus-mediated cell fusion, th e fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins of sim ian virus 5 (SV5), human parainfluenza virus 3 (HPIV-3), and Newcastle disease virus (NDV) were expressed individually or coexpressed in eit her homologous or heterologous combinations in CV-1 or HeLa-T4 cells, using the vaccinia virus-T7 polymerase transient expression system, Th e contribution of individual glycoproteins in virus-induced membrane f usion was examined by using a quantitative assay for lipid mixing base d on the relief of self-quenching (dequenching) of fluorescence of the lipid probe octadecyl rhodamine (R18) and a quantitative assay for co ntent mixing based on the cytoplasmic activation of a reporter gene, b eta-galactosidase. In these assays, expression of the individual F gly coproteins did not induce significant levels of cell fusion and no cel l fusion was observed in experiments when cells individually expressin g homologous F or HN proteins were mixed, However, coexpression of hom ologous F and HN glycoproteins resulted in extensive cell fusion, The kinetics of fusion were found to be very similar for all three paramyx oviruses studied, With NDV and HPIV-3, no cell fusion was detected whe n F proteins were coexpressed with heterologous HN proteins or influen za virus hemagglutinin (HA). In contrast, SV5 F protein exhibited a co nsiderable degree of fusion activity when coexpressed with either NDV or HPIV-3 HN or with influenza virus HA, although the kinetics of fusi on were two- to threefold higher when the homologous SV5 F and HN prot eins were coexpressed. Thus, these data indicate that among the paramy xoviruses tested, SV5 has different requirements for cell fusion.