Fusion inhibition: bioassay of type C viral protein.

Based on the observation that concentrated RD-114 virus directly induces fusion in a Rous sarcoma virus-transformed human glioma cell line, KC, an RD-114 virus protein was identified which had the property of inhibiting this fusion. The protein was irreversibly denatured by 2-mercaptoethanol, reacted with neutralizing sera to RD-114 virus, and eluted from guanidine agarose columns in a single peak in the 60 to 80,000 molecular-weight range. It does not prevent the fusion of KC cells by B-propiolactone-inactivated Sendai virus, and remained bound to KC cells even after extensive washing. It is suggested that the RD-114 fusion-inhibition factor is a viral surface protein which normally plays a role in virus attachment and is analogous to the 70,000-dalton glycoproteins (gp70) described for the murine Type C viruses.