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Mol. Cell. Biol., 03 1997, 1484-1489, Vol 17, No. 3
H Ikehata, S Kaneda, F Yamao, T Seno, T Ono and F Hanaoka
In temperature-sensitive (ts) mutants of mouse FM3A cells, the levels of
mutagenesis and survival of cells treated with DNA-damaging agents have
been difficult to assess because they are killed after their mutant
phenotypes are expressed at the nonpermissive temperature. To avoid this
difficulty, we incubated the ts mutant cells at the restrictive
temperature, 39 degrees C, for only a limited period after inducing DNA
damage. We used ts mutants defective in genes for ubiquitin-activating
enzyme (E1), DNA polymerase alpha, and p34(cdc2) kinase. Whereas the latter
two showed no effect, E1 mutants were sensitized remarkably to UV light if
incubated at 39 degrees C for limited periods after UV exposure.
Eighty-five percent of the sensitization occurred within the first 12 h of
incubation at 39 degrees C, and more than 36 h at 39 degrees C did not
produce any further sensitization. Moreover, while the 39 degrees C
incubation gave E1 mutants a moderate spontaneous mutator phenotype, the
same treatment significantly diminished the level of UV-induced
6-thioguanine resistance mutagenesis and extended the time necessary for
expression of the mutation phenotype. These characteristics of E1 mutants
are reminiscent of the defective DNA repair phenotypes of Saccharomyces
cerevisiae rad6 mutants, which have defects in a ubiquitin-conjugating
enzyme (E2), to which E1 is known to transfer ubiquitin. These results
demonstrate the involvement of E1 in eukaryotic DNA repair and mutagenesis
and provide the first direct evidence that the ubiquitin- conjugation
system contributes to DNA repair in mammalian cells.
Copyright © 1997, American Society for Microbiology
Incubation at the nonpermissive temperature induces deficiencies in UV resistance and mutagenesis in mouse mutant cells expressing a temperature-sensitive ubiquitin-activating enzyme (E1)
Department of Radiation Research, Tohoku University School of Medicine, Sendai, Japan.
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