Maintenance of 5-Methylcytosine in Mammalian Cells by Specific Correction of G/T Mispairs in Favor of Guanine

  • Thomas C. Brown
  • Josef Jiricny


We have developed a way of introducing specific mispairs into the genome of Simian Virus 40 and of determining the fate of the mispaired bases in simian cells. Mispairs are introduced into viral DNA within the intron of the gene coding for the large T antigen. Each DNA molecule harbors a single mispair in a defined orientation. Transfection of mismatch-containing SV40 DNA into host cells yields plaques, each corresponding to a productive infection initiated by a single viral DNA molecule. Determination of the DNA sequence at the site of the mispair reveals whether correction occured and what the repair products are. In this chapter we describe the correction of G/T mispairs. Mismatched G/T pairs arise spontaneously through the deamination of 5-methylcytosine (mC) to form thymine. Our results (Brown and Jiricny, 1987) indicate that G/T mispairs are corrected with extremely high efficiency and nearly always in favor of guanine. This biased correction of G/T mispairs thus restores G/C pairs lost through mC deamination.


Mismatch Repair Individual Plaque Mismatch Correction Mispaired Base TaqI Site 
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Copyright information

© Springer Science+Business Media New York 1989

Authors and Affiliations

  • Thomas C. Brown
    • 1
  • Josef Jiricny
    • 1
  1. 1.Friedrich Miescher InstituteBaselSwitzerland

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