The human mismatch-specific thymine DNA glycosylase gene, TDG, encodes a 60-kDa polypeptide able to correct G/T mispairs arising from the deamination of 5-methylcytosine. We localized by FISH three different TDG-related λ genomic clones, λ8, λ11, and λ12 on chromosome 12. PCR and sequence analyses revealed that only λ11, localized at 12q24.1, contained the coding gene. We characterized the intron-exon boundaries of the portion of the gene contained in the λ clone and identified a CA dinucleotide repeat in one intron. Northern blot analysis showed that TDG is expressed at approximately the same level in all human tissues analyzed. SSCP analysis of 50 tumor and corresponding normal tissue DNAs from lung cancer patients did not reveal the presence of any functional mutation. An abnormal SSCP pattern in one sample proved to be a polymorphism after sequencing and RFLP analysis.
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