Abstract
Optimal conditions for the detection of complex RNA sequences in individual cells by in situ hybridization have been determined by using in vitro cultured quail embryonic cells infected with Rous sarcoma virus and a single-stranded 3H-cDNA probe of high specific activity complementary to the RSV genome. It is shown that fixation of target tissue can be suitably achieved by using glutaraldehyde at low concentration, and subjecting cytological preparations to heat post-fixation treatment. Conditions for removing unhybridized radioactive probe molecules by means of S1 nuclease are reported.