title: The purification of a mismatch-specific thymine-DNA glycosylase from HeLa cells.
abstract: G/T mispairs that arise in the DNA of higher eukaryotes as a result of spontaneous hydrolytic deamination of 5-methylcytosine to thymine must be corrected to G/C pairs. We describe here the purification to apparent homogeneity of the enzyme that initiates this repair process by excising the mispaired thymine from the hetero-duplex to generate an apyrimidinic site. The enzymatic activity could be attributed to a 55-kDa polypeptide, which was purified from extracts of HeLa cells by a combination of conventional and DNA-affinity chromatography. The enzyme is a mismatch-specific thymine-DNA N-glycosylase, capable of hydrolyzing the carbon-nitrogen bond between the sugar-phosphate backbone of the DNA and a mispaired thymine. In addition to the G/T, the enzyme can remove thymine also from C/T and T/T mispairs in the order G/T >> C/T > T/T. It has no detectable endonucleolytic activity on apyrimidinic sites and does not catalyze the removal of thymine from A/T pairs or from single-stranded DNA.
authors.affiliation: Department of Biochemistry, Istituto di Richerche di Biologia Molecolare P. Angeletti, Rome, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Neddermann
authors.forename: J
authors.initials: J
authors.lastname: Jiricny
mesh_terms: D001483:Base Sequence; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004247:DNA; D004260:DNA Repair; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004591:Electrophoresis, Polyacrylamide Gel; D004706:Endodeoxyribonucleases / Q000302:isolation & purification* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009692:Nucleic Acid Heteroduplexes; D013379:Substrate Specificity
chemical_list: D009692:Nucleic Acid Heteroduplexes; D004247:DNA; D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer)