Active mammalian replication origins are associated with a high-density cluster of (m)CpG dinucleotides

作者：Rein T^*; Zorbas H; DePamphilis ML

来源：Molecular and Cellular Biology, 1997, 17(1): 416-426.

DOI：10.1128/mcb.17.1.416

ori-beta is a well-characterized origin of bidirectional replication (OBR) located similar to 17 kb downstream of the dihydrofolate reductase gene in hamster cell chromosomes. The similar to 2-kb region of ori-beta that exhibits greatest replication initiation activity also contains 12 potential methylation sites in the form of CpG dinucleotides, To ascertain whether DNA methylation might play a role at mammalian replication origins, the methylation status of these sites was examined with bisulfite to chemically distinguish cytosine (C) from 5-methylcytosine (C-m), All of the CpGs were methylated, and nine of them were located within 356 hp flanking the minimal OBR, creating a high-density cluster of (m)CpGs that was similar to 10 times greater than average for human DNA. However, the previously reported densely methylated island in which all cytosines were methylated regardless of their dinucleotide composition was not detected and appeared to he an experimental artifact, ti second OBR, located at the 5' end of the RPS14 gene, exhibited a strikingly similar methylation pattern, and the organization of CPG dinucleotides at other mammalian origins revealed the potential for high-density CpG methylation, Moreover, analysis of bromodeoxyuridine-labeled nascent DNA confirmed that active replication origins were methylated. These results suggest that a high-density cluster of (m)CpG dinucleotides may play a role in either the establishment or the regulation of mammalian replication origins.

• 出版日期1997-1