The effect of DNA methylation on the transcriptional activity of the hamster adenine phosphoribosyltransferase (aprt) and the herpes thymidine kinase (tk) genes has been investigated. By using M13 constructs containing these gene sequences, specific segments of each gene were methylated in vitro by restriction fragment primer-directed second-strand synthesis using the substrate 2'-deoxy-5-methyl-cytidine triphosphate (dmCTP). These hybrid-methylated molecules were inserted into mouse Ltk- cells by DNA-mediated cotransfer. In all cases, the integrated sequences retained the in vitro-directed methylation pattern. The aprt gene was inhibited by CpG methylation in the 5' region but was unaffected by methylation at the 3' end or in adjacent M13 sequences. In contrast to this, DNA methylation in both the 5' promoter region and the 3' structural region of the tk gene had a strong inhibitory effect. This suggests that this modification may affect transcription by mechanisms that do not involve the direct alteration of recognition sequences for RNA polymerase.
CpG islands (CGIs) are dense clusters of CpG sequences that punctuate the CpG-deficient human genome and associate with many gene promoters. As CGIs also differ from bulk chromo...
The mechanism whereby the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) is silenced in repair-deficient (Mer-) human tumor cells is unknown. The role of methy...
Mutations in the p53 gene are the most common genetic alterations observed in many inherited and sporadic forms of human cancer. Recent studies indicate that wild-type p53 may b...
DNA methylation plays an important role in biological processes in human health and disease. Recent technological advances allow unbiased whole-genome DNA methylation (methylome...
CpG dinucleotides are unevenly distributed in the vertebrate genome. Bulk DNA is depleted of CpGs and most of the cytosines in the dinucleotide in this fraction are methylated. ...
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