Sensitive immunological detection of translation products in SV40 plaques

A simple and sensitive in situ radioimmunoassay, using simian virus 40 (SV40) proteins as a model, has been developed for the detection of specific translation products of foreign genes cloned in viral vectors. This assay is based on the coupling of all proteins in viral plaques to diazophenylthioether (DPT)-paper. Specific proteins bound to the filter are detected by autoradiography after sequential incubation with (i) unfractionated and unlabeled specific antiserum and (ii) 125I-labeled protein A from Staphylococcus aureus. This assay detects SV40-specific proteins in individual plaques as early as 42 h after infection and its sensitivity limit is below 5 x 10(8) molecules of the major SV40 capsid protein, VP1.