Reverse Transcriptase Assay: The reverse transcriptase assay is performed 
according to the method of Goff et. al. Briefly, 10 ul of viral supemate is 
added to a 50 ul reaction mixture yielding a final concentration of 50 mM Tris- 
hydrochloride , pH8.3; 20 mM dithiothreitol ; 0.6 mM MnCl 2 ; 60 mM NaCl; 0.05% 
Nonidet P-40; 5 ug of oligodeoxvthymidylic acid/ml; 10 ug of polyriboadenylic 
acid per ml; and 10 uM alpha- [^P] dTTP (specific activity >400 Ci/mmole) . 
Reaction mixture is incubated for 2 hours at 37°C; and 10 ul is then blotted onto 
DEAE paper (DE-81). The paper is washed 5 times in 2x SSC (5 min at room 
temperature) , then 2 times in 95% ethanol for 1 min. The paper is air dried and 
autoradiographs are taken. 
Haapala, D.K., Robey, W.G., Oroszlan, and Tsai, W.P. (1985) Isolation from cats 
of an endogenous type C virus with a novel envelope glycoprotein. J. Virol. 53, 
827-833. 
Maniatis, T. , Fritsch, E.F., Sambrook, J. Molecular Cloning . Cold Spring Harbor 
Laboratory, Cold Spring Harbor, N.Y. 
Goff, S., Traktman, P., and Baltimore D. (1981) Isolation and properties of 
Moloney murine leukemia virus mutants: use of a rapid assay fdr release of virion 
reverse transcriptase. J. Virol. 38, 239-248. 
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