Volume 271, Number 38, Issue of September 20, 1996 pp. 22937-22940
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

---

COMMUNICATION:
Methylation of Expanded CCG Triplet Repeat DNA from Fragile X Syndrome Patients Enhances Nucleosome Exclusion

(Received for publication, June 27, 1996)

From the Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7295

Long tracts of CCG trinucleotide or CCGNN pentanucleotide repeats in DNA have previously been shown to resist assembly into nucleosomes. This may provide a molecular explanation for the nature of certain rare, folate-sensitive fragile sites in human chromosomes that contain expanded CCG triplet tracts. Further, it is known that methylation of CpG dinucleotides at or near these fragile sites enhances the fragile phenotype. Here DNAs containing 76 tandem CCG triplets or 48 CCGNN pentanucleotide repeats were methylated with SssI methylase at three different levels of methylation. Using competitive nucleosome reconstitution/gel shift assays, the ability of these DNAs and a mixed sequence DNA from the pUC19 plasmid were compared in their ability to assemble into nucleosomes. DNA methylation had no significant effect on nucleosome formation over the pUC 19 fragment. However, the highly methylated DNAs containing 76 CCG triplets or 48 CCGNN pentanucleotide repeats were 2.0 ± 0.2-fold and 2.1 ± 0.3-fold less efficient in nucleosome assembly than the respective unmethylated forms, and 4.4 ± 0.4-fold and 12.6 ± 1.6-fold less efficient than a pUC19 fragment of similar length.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				D. J. Mulvihill, K. N. Edamura, K. A. Hagerman, C. E. Pearson, and Y.-H. Wang Effect of CAT or AGG Interruptions and CpG Methylation on Nucleosome Assembly upon Trinucleotide Repeats on Spinocerebellar Ataxia, Type 1 and Fragile X Syndrome J. Biol. Chem., February 11, 2005; 280(6): 4498 - 4503. [Abstract] [Full Text] [PDF]

				D. J. Mulvihill and Y.-H. Wang Two Breakpoint Clusters at Fragile Site FRA3B Form Phased Nucleosomes Genome Res., July 1, 2004; 14(7): 1350 - 1357. [Abstract] [Full Text] [PDF]

				P. Weisman-Shomer, E. Cohen, I. Hershco, S. Khateb, O. Wolfovitz-Barchad, L. H. Hurley, and M. Fry The cationic porphyrin TMPyP4 destabilizes the tetraplex form of the fragile X syndrome expanded sequence d(CGG)n Nucleic Acids Res., July 15, 2003; 31(14): 3963 - 3970. [Abstract] [Full Text] [PDF]

				K. Nichol and a. C. E. Pearson CpG Methylation Modifies the Genetic Stability of Cloned Repeat Sequences Genome Res., August 1, 2002; 12(8): 1246 - 1256. [Abstract] [Full Text] [PDF]

				Y. Y. Hsu and Y.-H. Wang Human Fragile Site FRA16B DNA Excludes Nucleosomes in the Presence of Distamycin J. Biol. Chem., May 3, 2002; 277(19): 17315 - 17319. [Abstract] [Full Text] [PDF]

				B. S. Balakumaran, C. H. Freudenreich, and V. A. Zakian CGG/CCG repeats exhibit orientation-dependent instability and orientation-independent fragility in Saccharomyces cerevisiae Hum. Mol. Genet., January 1, 2000; 9(1): 93 - 100. [Abstract] [Full Text] [PDF]