Detection of GP64 proteins by western blot. Concentrated viral vectors pseudotyped with wild type GP64, Sendai-GP64, and Sendai-spGP64 were subjected to western blotting and GP64 was detected using a monoclonal antibody. Lane 1 wtGP64, Lane 2 Sendai-GP64, Lane 3 Sendai-spGP64. The lane with wtGP64 pseudotyped virus shows strong reactivity at the expected size, 64 kDa. The higher molecular mass band likely represent GP64 trimers. The lane with Sendai-spGP64 pseudotyped virus shows reactivity at the expected size but at a much lower level. The lower molecular mass bands in the lanes with Sendai-GP64 and Sendai-spGP64 likely represent aspecific reactivity.