title: The rate of hydrolytic deamination of 5-methylcytosine in double-stranded DNA.
abstract: The modified base, 5-methylcytosine, constitutes approximately 1% of human DNA, but sites containing 5-methylcytosine account for at least 30% of all germline and somatic point mutations. A genetic assay with a sensitivity of 1 in 10(7), based on reversion to neomycin resistance of a mutant pSV2-neo plasmid, was utilized to determine and compare the deamination rates of 5-methylcytosine and cytosine in double-stranded DNA for the first time. The rate constants for spontaneous hydrolytic deamination of 5-methylcytosine and cytosine in double-stranded DNA at 37 degrees C were 5.8 x 10(-13) s-1 and 2.6 x 10(-13) s-1, respectively. These rates are more than sufficient to explain the observed frequency of mutation at sites containing 5-methylcytosine and emphasize the importance of hydrolytic deamination as a major source of human mutations.
authors.affiliation: Department of Biochemistry and Molecular Biology, USC/Norris Comprehensive Cancer Center, School of Medicine, Los Angeles 90033.
authors.forename: J C
authors.initials: JC
authors.lastname: Shen
authors.forename: W M
authors.initials: WM
authors.lastname: Rideout
authors.forename: P A
authors.initials: PA
authors.lastname: Jones
mesh_terms: D044503:5-Methylcytosine; D001483:Base Sequence; D003596:Cytosine / Q000031:analogs & derivatives* / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D015257:DNA-Cytosine Methylases / Q000378:metabolism; D003641:Deamination; D006868:Hydrolysis; D007700:Kinetics; D008745:Methylation; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010957:Plasmids; D013816:Thermodynamics; D014170:Transformation, Genetic
chemical_list: D044503:5-Methylcytosine; D003596:Cytosine; D004247:DNA; C029641:DNA modification methylase HpaII; D015257:DNA-Cytosine Methylases