A New Look at the Mode of Action of Polyoma and Related Tumor Viruses

A Simplifying Concept in Tumor Virology: Virus-specific "Pleiotropic Effectors"

“…2), 0.5-1% of the nuclei exhibit by 12 hours a weak immunofluorescence reaction for intranuclear polyoma-specific T antigen; the number of positive nuclei (and also the intensity of the immunofluorescence reaction) thereafter rapidly increase, and by 20-24 hours virtually all cells contain T antigen. In cells where the immunofluorescence reaction for T antigen has reached a relatively high intensity, a rather sudden increase in nucleolar size can be observed, which is the morphological expression of polyoma-induced stimulation of cellular RNA synthesis (see below and Weil and K~ra 1970;Weil et al 1974). As determined by autoradiography, polyoma-induced (cellular and viral) DNA synthesis begins in a very small fraction of cells (< 1%) around 13 hours; thereafter the number of DNA-synthesizing cells rapidly increases, reaching a maximum plateau 25-30 hours after infection, when 70-80% of the cells synthesize DNA (P6tursson and Weil 1968;Well and K~ra 1970).…”

“…From sedimentation velocity analyses performed under denaturing conditions in DMSO gradients, the molecular weight of SV40-and polyoma-specific 19S RNA was estimated to be about 7 x 10 ~ daltons, corresponding to the transcript of 40-45% of one strand of SV40 or polyoma DNA (Buetti 1974;Weil et al 1974). From more recent experimental results, Khoury has concluded that during the abortive infection of mouse cells with SV40, mainly the "early region" of SV40 DNA is transcribed into stable RNA (pers.…”

“…The results led to the conclusion that polyoma and SV40 act primarily as endogenous mitogens and that virusinduced replication of the host cell chromatin is a necessary, though insufficient, condition for synthesis of viral progeny DNA (Weil and Khra 1970;May et al 1973;Seebeck and Weil 1974;Weil et al 1974).…”

“…3 x l0 s daltons). Polyoma induces different types of tumors in mice and related rodents, while SV40 induces subcutaneous tumors, leukemias and lymphomas in hamsters (Eddy 1964(Eddy , 1969Diamandopoulos 1973); both viruses can "transform" tissue culture cells; transformed cells contain integrated viral DNA, synthesize virus-specific RNA and T antigen, exhibit surface alterations (e.g., virus-specific transplantation antigens) and an increased potential for growth under various selective conditions; last but not least, infection of permissive cells leads to the production of progeny virus containing 6 or 7 structural polypeptides which, if specified by the viral genome, would require its entire coding capacity (for details, see Defendi 1966;Tooze 1973;Weil et al 1974;Weil 1975).…”

DNA-Binding Proteins in Mouse Cells Infected with Polyoma Virus

“…To prevent viral DNA replication and expression of late viral functions, infection of permissive mouse cells 3T6 was carried out in the presence of 5-fluorodeoxyuridine (15 ¡¿g/ml), which does not seem to interfere with poly oma early gene expression [20]; in parallel, mock-infected cells were similarly grown and treated. Cells were extracted at high ionic strength (0.6 M NaCl), in order to dissociate most nucleoprotein complexes, and then the crude extract was chromatographed, as described by Alberts and Herricks [21], on DNA-cellulose (single-stranded:double-stranded, 1:1).…”