Defective virions in human adenovirus type 12

Purified preparations of human adenovirus type 12 showed two bands when subjected to isopycnic centrifugation in a density gradient of cesium chloride. Their density difference was about 0.003 g/ml, suggesting a small difference in their deoxyribonucleic acid to protein ratio. Virions with a lighter density can kill human KB cells and induce T antigen as efficiently as the heavy virions. However, they appeared incapable to form plaques. Two passages of the heavy infectious virions at low multiplicity of infection did not produce significant amounts of light virions; however, when it was passed at high multiplicity of infection, the light band became visible in a cesium chloride density gradient.