Nucleoprotein Complexes in Simian Virus 40-Infected Cells

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Abstract
When African green monkey kidney cells (BSC-1) were infected with simian virus 40 (SV40) and extracted with 0.25% Triton X-100 after exposure to 3H-thymidine, the 3H-SV40 deoxyribonucleic acid (DNA) was present in a form which had a sedimentation coefficient in sucrose gradients of 44S. The change from the sedimentation coefficient of purified SV40 DNA (21S) was shown to result from the association of the SV40 DNA in the Triton extracts with protein by means of sensitivity to Pronase digestion and labeling with 14C-amino acids. Short-term labeling experiments with 3H-thymidine demonstrated that SV40 DNA molecules in the course of replication (25S) were also present as nucleoprotein complexes in Triton-extracted material. Labeled DNA extracted with Triton in the form of nucleoprotein complexes was obtained in amounts which were quantitatively equivalent to the amounts extracted with deoxycholate in parallel experiments. This indicated that the newly synthesized pools of SV40 DNA may not occur as free DNA in the infected cell.