Abstract
Concentration of Rous sarcoma virus from tissue culture fluids with polyethylene glycol, with and without NaCl or dextran sulfate, resulted in significant and highly variable losses caused by entrapment of virus particles in proteinaceous debris. Treatment of concentrated preparations with Pronase greatly enhanced the recovery of virions. Maximum recovery of virus particles was obtained by the addition of 8% polyethylene glycol and 0.4 M NaCl to tissue culture fluids, followed by Pronase treatment of the concentrated virus preparations.