Abstract
It was demonstrated previously that polyoma pseudovirions (DNA fragments encapsidated by polyoma virus coats) are adsorbed to and uncoated by mouse-embryo cells. 24 hr after infection of secondary mouse-embryo cells with [(3)H]thymidine-labeled pseudovirus, 24% of the total radioactivity found in cells occurred in the nuclear fraction. This nuclear radioactivity represents pseudovirus DNA, as shown by its hybridization with mouse-embryo DNA. Since much of the radioactive material found in the nuclear fraction is sensitive to pancreatic DNase, it is available as uncoated DNA.24 hr after infection of human embryo cells with [(3)H]thymidine-labeled pseudovirions, 7% of the total cellular radioactivity is found in the nuclear fraction of the cells. That this radioactivity represents uncoated pseudoviral DNA was shown by sedimentation of the disrupted nuclear fraction through a neutral sucrose gradient. The pseudoviral DNA in the nuclear fraction has been nicked to some extent, as shown by the heterogeneity of the peaks found after sedimentation of the disrupted nuclear fraction through alkaline sucrose. The experiments demonstrate that polyoma pseudovirions deliver DNA to human cells.