Cyclobutane thymine dimers in a ras proto-oncogene hot spot activate the gene by point mutation.
ras proto-oncogenes with a cyclobutane-type thymine photodimer (cis-syn or trans-syn isomer) were constructed by replacement of a portion of the gene with a chemically synthesized fragment. When the genes were transfected by the calcium phosphate method into mouse NIH3T3 cells, they induced focus-formation, indicating that both photoproducts were mutagenic in mammalian cells. Sequence analysis of the ras gene fragments derived from the transformed cells showed that the genes were activated by a point mutation. The mutations detected most frequently were 3'-T-->A for the cis-syn isomer and 5'-T-->A for the trans-syn isomer. In contrast, a different trend of mutations was observed when a primer on a DNA template with a cis-syn dimer was extended in vitro by either DNA polymerase beta or alpha.
Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
H
H
Kamiya
N
N
Murata
T
T
Murata
S
S
Iwai
A
A
Matsukage
C
C
Masutani
F
F
Hanaoka
E
E
Ohtsuka
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002851:Chromatography, High Pressure Liquid; D003503:Cyclobutanes; D004262:DNA Restriction Enzymes; D011905:Genes, ras; D005822:Genetic Vectors; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009841:Oligonucleotides / Q000138:chemical synthesis; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011740:Pyrimidine Dimers; D014162:Transfection
D003503:Cyclobutanes; D009841:Oligonucleotides; D011740:Pyrimidine Dimers; D004262:DNA Restriction Enzymes