Cytological preparations of interphase nuclei and chromosomes from mouse 3T6 cells prepared at various times after infection with the murine sarcomaleukemia virus complex were hybridized with the [(3)H]DNA product of the viral RNA-directed DNA polymerase. While uninfected nuclei had an average of 4 autoradiographic grains, infected nuclei had 30 grains at 5 hr after infection and 63-65 grains at 11 and 25 hr. Virus-specific grains were localized in the chromocenters of interphase nuclei and were found also in the centromeric heterochromatin region of metaphase chromosomes. These findings provide evidence that the viral RNA-directed DNA polymerase functions to synthesize virus-specific DNA early after infection and that newly synthesized viral DNA rapidly becomes associated with or integrated into specific intranuclear sites.
Animals Autoradiography