Defective mouse sarcoma virus deficient in DNA polymerase activity

C-type RNA virus from hamster cells transformed in vitro by 1-B-D-arabinofuranosylcytosine

Evidence of type-C RNA viral activity in fetal hamster cells transformed in vitro by 1-B-D-arabinofuranosylcytosine (ara-C) after at least one in vivo passage is described. The virus possesses properties typical of other type-C RNA viruses, such as: a) morphology as determined with the electron microscope, b) presence of 70S RNA, c) enhanced expression following treatment with halogenated pyrimidines, d) group specific antigens of hamster type, and e) a buoyant density of 1.15 g per cm3. However, the virus particles are deficient in RNA-dependent DNA polymerase activity under conditions that easily detect Rauscher Leukemia virus and will infect neither hamster, rat, mouse, human nor rabbit cells. The possible role of this virus in chemical carcinogenesis of cultured hamster fetal cells is discussed.

Spontaneous mutation of RNA tumour viruses

There are 2 categories of spontaneously occurring avian and mammalian RNA tumour virus mutants: conditional and non-conditional. 1) Conditional mutants are able to replicate in or transform cells only under certain physiological conditions or in certain cells. RNA tumour virus temperature-sensitive mutants, focus-morphology mutants, and host range mutants are spontaneously formed. Some of these conditional mutants probably arise by point mutations in the viral genome. 2) Non-conditional mutants have genetic lesions that render them inactive under all conditions. There are non-conditional spontaneous RNA tumour virus mutants that are missing either the virion envelope glycoprotein or both the envelope glycoprotein and the virion DNA polymerase. These mutants cannot replicate or transform cells. Other spontaneous non-conditional mutants can replicate but are defective in their ability to transform fibroblastoid cells. These spontaneous transformation-defective mutants can have deletions in 10-20% of the genomic RNA. Conditional mutants with an altered host range occur at a high rate of approximately 1 mutation/50 infected cell generations during DNA-to-DNA information transfer. This type of conditional mutation requires cell replication but does not occur frequently either during the original synthesis of viral DNA (RNA-to-DNA information transfer) or during the transcription of progeny viral RNA from the (RNA-to-DNA information transfer) or during the transcription of progeny viral RNA from the DNA (DNA-to-RNA information transfer). Temperature-sensitive and focus-morphology mutants also have a high rate of spontaneous formation. Non-conditional mutants missing the viral envelope glycoprotein, DNA polymerase, or transformation gene, also appear to be spontaneously formed at a high rate. Normal avian and mammalian cells contain RNA tumour virus-related genes in their DNA. It is hypothesized that these endogenous RNA tumour virus-related genes in normal cells also have a high rate of spontaneous mutation and are involved in neoplastic processes.

Lack of serological relationship among DNA polymerases of avian leukosis-sarcoma viruses, reticuloendotheliosis viruses, and chicken cells

Antibodies against a large and a small DNA polymerase isolated from chicken embryos and against avian myeloblastosis virus DNA polymerase were used to study the serological relationships of the DNA polymerase activities of three avian systems with RNA and a DNA polymerase-avian leukosis-sarcoma viruses, reticuloendotheliosis viruses, and a fraction from uninfected chicken cells. The DNA polymerase activity of disrupted virions of all avian leukosis-sarcoma viruses tested was neutralized to the same extent by antibody against avian myeloblastosis virus DNA polymerase and was not neutralized by the antibodies against chicken cellular DNA polymerases. The viruses tested included induced leukosis viruses and Rous-associated virus-O. The DNA polymerase activity of disrupted virions of all of the reticuloendotheliosis viruses was not neutralized by any of the antibodies. The chicken endogenous RNA-directed DNA polymerase activity was neutralized partially or completely, in different experiments, by antibody against the small DNA polymerase isolated from chicken embryos, but was not neutralized by the other two antibodies.

Temperature-dependent expression of transformation by cold-sensitive mutant of murine sarcoma virus

Morphological transformation of normal rat kidney cells by a murine sarcoma virus was found to be cold-sensitive. Cells transformed by the virus expressed their transformed phenotype at the permissive temperature (39 degrees ) but not at the nonpermissive temperature (33 degrees ), as judged by the criteria of morphological changes and colony-forming ability on monolayers of normal rat kidney cells. Cold-sensitive expression of transformation was specific for focus-derived normal rat kidney cells transformed by the virus, readily reversible, and not lost during serial propagation of the cells. The genome of the murine sarcoma virus can be rescued by superinfection with Moloney leukemia virus at the permissive or nonpermissive temperature, and the rescued virus exhibited the same cold-sensitive properties as the original transforming virus. These results suggest that maintenance of the transformed state is continuously dependent on a cold-sensitive viral function.