Mutants of the paramyxovirus SV5 fusion protein: regulated and extensive syncytium formation.

To study paramyxovirus-mediated cell fusion it would be advantageous to express in a cell a single protein that could cause regulated syncytium formation at neutral pH following a specific activation signal. We have constructed two SV5 fusion (F) protein mutants that contain three arginine residues in the cleavage site and two separate glycine to alanine changes in the fusion peptide. The mutants were expressed in CV-1 cells using an SV40 recombinant virus vector. The mutant F proteins required addition of exogenous trypsin to cleave F0 to F1 and F2. Massive syncytium formation occurred within 2-4 hr following addition of trypsin to the SV40 recombinant F virus-infected CV-1 cells.