title: DNA synthesis in polyoma virus infection. IV. Mechanism of formation of closed-circular viral DNA deficient in superhelical turns.
abstract: A marked reduction in the rate of viral DNA synthesis is accompanied by an alteration to the superhelicity of progeny DNA in polyoma virus-infected cells in which protein synthesis has been inhibited by cycloheximide. Viral DNA molecules formed in the presence of cycloheximide consist predominantly of closed-circular monometric species (referred to as form Ic) characterized by a decreased superhelix density, corresponding to deltasigmao = 0.0195, as compared to form I DNA by propidium diiodide-cesium chloride isopycnic analysis. Form Ic is synthesized on pre-existing form I templates without the intervention of progeny form I as an intermediate. It is concluded that inhibition of protein synthesis results in the alteration of some process in the closure of daughter DNA that leads to a marked reduction of superhelical turns of progeny molecules. About two-thirds of form Ic molecules return to the form I conformation upon reversal of cycloheximide inhibition by a mechanism independent of DNA replication.
mesh_terms: D004261:DNA Replication; D004270:DNA, Circular / Q000032:analysis / Q000096:biosynthesis*; D004279:DNA, Viral / Q000032:analysis / Q000096:biosynthesis*; D009690:Nucleic Acid Conformation; D011120:Polyomavirus / Q000032:analysis / Q000378:metabolism*; D014764:Viral Proteins / Q000096:biosynthesis
chemical_list: D004270:DNA, Circular; D004279:DNA, Viral; D014764:Viral Proteins