Radioimmunoassay for infectious primate retrovirus reverse transcriptase: Characterization, comparison with conventional immunologic assays and applicability to cellular extracts

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Abstract
SSV reverse transcriptase (RT) was purified to homogeneity and used in a radioimmunoassay. Following iodination, the homogeneity of the protein and its identity with RT were confirmed by several criteria: (I) its molecular weight on an SDS‐polyacrylamide gel; (2) its precipitation by anti‐SSV RT but not by antisera to other SSV proteins; (3) its cross‐reactivity in RIA with antisera to other retroviral polymerases; (4) its competition in RIA by active homogeneous SSV RT but not by other purified SSV proteins; and (5) its competition in RIA by only those fractions from a poly(U)‐Sepharose column possessing SSV RT activity. Competition of the labelled probe with disrupted retroviruses of the infectious primate group showed that, while a homologous RIA detected only type‐specific enzyme determinants, it did not distinguish the various woolly‐gibbon retroviral DNA polymerases. A more broadly reactive heterologous assay utilizing an antiserum to R‐MuLV RT detected groupbut not interspecies‐specific enzyme determinants. A comparison of immunologic assays for RT showed that: (I)highly purified RT is not essential for reliable results in enzyme neutralization or enzyme binding assays; (2) the greater sensitivity of enzyme binding compared to enzyme neutralization assays is a function of the antibody, not of the antigen. Competition RIAs using extracts of virus‐infected cells showed that infectious primate retrovirus RT could be measured in a crude system and that cellular DNA polymerares α,β and γ did not compete with the labelled probe.