Synthesis of multimeric polyoma virus DNA in mouse L-cells: role of the tsA1S9 gene product

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Abstract
Several different forms of progeny viral DNA can be identified in polyoma virus (Py)-infected mouse L cells. The majority comprise mature form 1 superhelical DNA and the circular, double-stranded theta replicating intermediates in which the progeny DNA strands never exceed the unit genome length of the template. There is formed, in addition, a minority fraction of multimeric, linear, double-stranded Py DNA molecules that sediment heterogeneously at 28-35S and > 35S. Restriction enzyme analysis of these large Py DNA molecules reveals them to be tandem arrays of multiple unit genome lengths, covalently linked head to tail. It is estimated that the 28-35S multimeric DNA has an average size of .apprx. 20 megadaltons, made up of 6-20 Py genome units. The > 35S Py DNA is larger. Kinetic analysis indicates that formation of the monomeric progeny viral DNA and the 28-35S multimeric Py DNA reaches a peak at .apprx. 35-36 h postinfection. Synthesis of the very large linear molecules of > 35S is first detected after this interval and continues thereafter. The de novo synthesis of all of these progeny Py DNA moelcules proceeds apparently normally in Py-infected tsA1S9 mouse L cells incubated at 38.5.degree. C under conditions which restrict normal cellular DNA replication. Evidently, the cellular DNA topoisomerase II activity, encoded in the tsA1S9 locus, is not required for de novo formation of any form of Py DNA. The total amount made and the rate of synthesis of the large MW Py DNA are affected very late in temperature-inactivated tsA1S9 cells.