Absence of an unusual "densely methylated island" at the hamster dhfr ori-beta

An unusual "densely methylated island" (DMI), in which all cytosine residues are methylated on both strands for 127-516 base pairs, has been reported at mammalian origins of DNA replication. This report had far-reaching implications in understanding of DNA methylation and DNA replication....

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Bibliographic Details
Published in:The Journal of biological chemistry 1997-04, Vol.272 (15), p.10021-10029
Main Authors: Rein, T, Natale, D A, Gärtner, U, Niggemann, M, DePamphilis, M L, Zorbas, H
Format: Article
Language:English
Subjects:
Animals
Base Sequence
Blotting, Southern
CHO Cells
Cricetinae
Cytosine - analogs & derivatives
Cytosine - analysis
DNA Methylation
Flow Cytometry
Hydrazines - pharmacology
Manganese Compounds - pharmacology
Molecular Sequence Data
Oxides - pharmacology
Polymerase Chain Reaction
Replication Origin
Restriction Mapping
Tetrahydrofolate Dehydrogenase - genetics
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Summary:An unusual "densely methylated island" (DMI), in which all cytosine residues are methylated on both strands for 127-516 base pairs, has been reported at mammalian origins of DNA replication. This report had far-reaching implications in understanding of DNA methylation and DNA replication. For example, since this DMI appeared in about 90% of proliferating cells, but not in stationary cells, it may regulate origin activation. In an effort to confirm and extend these observations, the DMI at the well characterized ori-beta locus 17 kilobases downstream of the dhfr gene in chromosomes of Chinese hamster ovary cells was checked for methylated cytosines in genomic DNA. The methylation status of this region was examined in randomly proliferating and stationary cells and in cell populations enriched in the G1, S, or G2 + M phases of their cell division cycle. DNA was subjected to 1) cleavage by methylation-sensitive restriction endonucleases, 2) hydrazine modification of cytosines followed by piperidine cleavage, and 3) permanganate modification of 5-methylcytosines (mC) followed by piperidine cleavage. The permanganate reaction is a novel method for direct detection of mC residues that complements the more commonly used hydrazine method. These methods were capable of detecting mC in 2% of the cells. At the region of the proposed DMI, only one mC at a CpG site was detected. However, the ori-beta DMI was not detected in any of these cell populations using any of these methods.
ISSN:0021-9258
DOI:10.1074/jbc.272.15.10021