Cyclobutane thymine dimers in a ras proto-oncogene hot spot activate the gene by point mutation

Nucleic Acids Res. 1993 May 25;21(10):2355-61. doi: 10.1093/nar/21.10.2355.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Chromatography, High Pressure Liquid
  • Cyclobutanes*
  • DNA Restriction Enzymes
  • Genes, ras*
  • Genetic Vectors
  • Mice
  • Molecular Sequence Data
  • Mutagenesis*
  • Oligonucleotides / chemical synthesis
  • Point Mutation
  • Polymerase Chain Reaction
  • Pyrimidine Dimers*
  • Transfection


  • Cyclobutanes
  • Oligonucleotides
  • Pyrimidine Dimers
  • DNA Restriction Enzymes