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K Dixon

Publications and source records attributed to K Dixon.

118 records · Page 7Linked to original sources
PubMedDate not supplied

Studies on direct and indirect effects of DNA damage on mutagenesis in monkey cells using an SV40-based shuttle vector.

We are using an SV40-based shuttle vector, pZ189, to study mechanisms of mutagenesis in mammalian cells. The vector can be treated with mutagens in vitro and replicated in animal cells; resulting mutants can be selected and amplified in bacteria for DNA sequencing. This versatile vector system has allowed us to explore several different questions relating to the mutagenic process. We have studied the direct effects of template damage caused by UV or benzo[a]pyrene diolepoxide by treating vector DNA with these agents and then replicating the damaged DNA in monkey cells. Mutational mechanisms were deduced from the spectrum of mutations induced in the supF target gene of the vector DNA. To study the role of indirect effects of DNA damage on mutagenesis in mammalian cells, we have treated the cells and the vector DNA separately with DNA-damaging agents. We find that pretreatment of cells with DNA-damaging agents, or with conditioned medium from damaged cells, causes an enhancement of mutagenesis of a UV-damaged vector. Thus, DNA damage can act indirectly to enhance the mutagenic process. We also have preliminary evidence that pZ189 can be used in an in vitro DNA replication system to study the process of mutation fixation on the biochemical level. We believe that the pZ189 vector will prove to be as useful for in vitro studies of mutational mechanisms as it has been for in vivo studies.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMedDate not supplied

Induction of a novel damage-specific DNA binding protein correlates with enhanced DNA repair in primate cells.

Pretreatment of mammalian cell with DNA-damaging agents, such as UV light or mitomycin C, but not the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA), results in the enhanced repair of subsequently transfected UV-damaged expression vectors. To determine the cellular factors that are responsible for this enhancement, we have used a modified gel retardation assay to detect the proteins that interact with damaged DNA. We have identified a constitutive DNA binding protein in extracts from primate cells that has a high affinity for UV-irradiated double-stranded DNA. Cells pretreated with UV light, mitomycin C, or aphidicolin, but not TPA or serum starvation, have higher levels of this damage-specific DNA binding (DDB) protein. These results suggest that the signal for induction of DDB protein can either be damage to the DNA or interference with cellular DNA replication. The induction of DDB protein varies among primate cells with different phenotypes: (1) virus-transformed repair-proficient cells have partially or fully lost the ability to induce DDB protein above constitutive levels; (2) primary cells from repair-deficient xeroderma pigmentosum (XP) group C, and transformed XP groups A and D, show constitutive DDB protein, but do not show induced levels of this protein 48 h after UV; and (3) primary and transformed repair-deficient cells from one XP E patient are lacking both the constitutive and the induced DDB activity. The correlation between the induction of the DDB protein and the enhanced repair of UV-damaged expression vectors implies the involvement of the DDB protein in this inducible cellular response.

Animals↗