Level Of Genetic Instability Research Articles

Transformation and radiosensitivity of human diploid skin fibroblasts transfected with activated ras oncogene and SV40 T-antigen.

Three normal human diploid cell strains were transfected with an activated Ha-ras oncogene (EJ ras) or SV40 T-antigen. Multiple clones were examined for morphological alterations, growth requirements, ability to grow under anchorage independent conditions, immortality and tumorigenicity in nude mice. Clones expressing SV40 T-antigen alone or in combination with ras protein p21 were significantly radioresistant as compared with their parent cells or clones transfected with the neo gene only. This radioresistant phenotype persisted in post-crisis, immortalized cell lines. Cells transfected with EJ ras alone showed no morphological alterations nor significant changes in radiosensitivity. Cell clones expressing ras and/or SV40 T-antigen showed a reduced requirement for serum supplements, an increase in aneuploidy and chromosomal aberrations, and enhanced growth in soft agar as an early cellular response to SV40 T-antigen expression. The sequential order of transfection with SV40 T-antigen and ras influenced radio-sensitivity but not the induction of morphological changes. These data suggest that expression of the SV40 T-antigen but not activated Ha-ras plays an important role in the radiosensitivity of human diploid cells. The radioresistant phenotype in SV40 T transfected cells was not related to the enhanced level of genetic instability seen in pre-crisis and newly immortalized cells, nor to the process of immortalization itself.

Genetic instability and hypervariability in Streptomyces ambofaciens: towards an understanding of a mechanism of genome plasticity

Many Streptomyces species exhibit a very high degree of genetic instability which is usually manifested as genomic rearrangements such as large deletions. In Streptomyces ambofaciens DSM40697, two levels of genetic instability were previously described: (i) a basic genetic instability similar to that reported for other strains, and (ii) hypervariability, a phenomenon that we believe to be a new aspect of instability closely associated with DNA amplification. A large DNA region undergoes deletions, amplifications and large genomic changes strictly associated with both aspects of genetic instability. The genetic and molecular analyses of the different aspects of genetic instability allow us to propose that they result from a cascade of molecular events and to investigate the relationships between genetic instability phenomena and genome fluidity.

Temperature-sensitive mutants of influenza A virus. Transfer of the two ts-1A2 ts lesions present in the Udorn/72-ts-1A2 donor virus to the influenza A/Alaska/6/77 (H3N2) wild type virus.

The Udorn/72-ts-1A2 temperature-sensitive influenza A virus has a 37 degrees C shutoff temperature and a ts mutation on the genes coding for the P1 and P3 proteins. This ts donor virus was produced with the expectation that the transfer of its two ts genes would regularly and predictably attenuate each new variant of influenza A virus. It had previously been mated with the A/Victoria/75 (H3N2) virus and five Vic/75-ts-1A2 rcombinants were isolated that had both ts-1A2 ts genes and in vitro and in vivo genetic and biological properties similar to their Udorn/72-ts-1A2 parent. The present study was designed to determine if the acquisition of the two ts-1A2 ts genes would also confer a specific level of attenuation on the influenza A/Alaska/6/77 (H3N2) wild type virus. Fifteen recombinant Alaska/77-ts-1A2 viruses were isolated and characterized genetically for the number and location of ts mutations. These clones were also studied for their level of replication and genetic stability in hamsters. Four recombinants possessed both of the ts-1A2 mutations and had a 37 degrees C shutoff temperature for plaque formation. Two recombinants possessed only a ts P1 gene and had either a 38 degrees C or 39 degrees C shutoff temperature. The remaining nine clones had the ts P3 gene and a shutoff temperature of 37 degrees C, 38 degrees C or 39 degrees C. Each of the four 37 degrees C shutoff temperature recombinants that possessed both ts P1 and P3 genes were restricted at least 10,000-fold in replication in the hamster's lung and approximately 100-fold in the nasal turbinates compared to the level of replication of wild type virus in these sites. All isolates from these animals retained the ts phenotype. The level of replication in vivo of the ts P1 and P3 segregants was related to their shutoff temperature of plaque formation in vitro, e.g. the 38 degrees C ts P3 segregant was less restricted in replication in the lungs than a 37 degrees C ts P3 segregant. All isolates from animals infected with the ts P3 segregants were ts, whereas a low level of genetic instability was detected for one of the ts P1 segregants. Since ten independent ts-1A2 recombinants (one Udorn/72, 5 Victoria/75 and 4 Alaska/77) with both ts-1A2 mutations exhibited the same genetic and biologic properties, it is likely that these ts P1 and P3 genes were the prime determinants of attenuation and could effect a similar level of attenuation in other influenza A viruses within the H3N2 subtype.