Analysis of the Molecular Forms of Simian Virus 40 Deoxyribonucleic Acid Synthesized in Cycloheximide-Treated Cell Cultures

Cycloheximide addition at various times from 24 to 36 hr after virus infection markedly inhibits the rate of simian virus 40 (SV40) deoxyribonucleic acid (DNA) synthesis in monkey kidney (CV-1) cultures. To determine whether superhelical (form I) SV40 DNA was synthesized in the cycloheximide-inhibited cultures, extracts were prepared by the method of Hirt from cultures labeled with 3H-thymidine (3H-dT) and were analyzed by cesium chloride-ethidium bromide (CsCl-EtBr) equilibrium centrifugation and by velocity sedimentation in neutral sucrose gradients. When control or cycloheximide-treated cultures were labeled for 2 or 4 hr with 3H-dT at 36 or 37 hr after infection, 71 to 83% of the radioactivity soluble in 1 m NaCl was detected in closed-circular SV40 DNA (form I). Cycloheximide treatment did not generate an increase of higher multiple circular forms of SV40 DNA. In pulse-chase experiments with or without cycloheximide treatment, radioactivity first appeared in nicked molecular forms sedimenting faster than open-circular SV40 DNA (form II), and then was chased into superhelical form I SV40 DNA. These results suggest that in cycloheximide-treated SV40-infected cultures: (i) polynucleotide ligase concentrations are adequate, and (ii) duplication errors causing formation of circular oligomers of SV40 DNA are not enhanced.

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