Tissue specificity and clustering of methylated cystosines in bovine satellite I DNA.
The positions of all 5-methylcytosine (mC) residues in bovine satellite I DNA were determined by sequence analysis of native purified satellite I DNAs from three bovine tissues as well as from cloned DNA. The EcoRI cleavage units from thymus and liver were found to contain 1,402 residues; that from brain contained 1,401 residues. Satellite I DNA from thymus contained a total of 5.0% mC, whereas that from liver and brain contained 4.4% and 2.6% mC, respectively. Thus, the extent of methylation of this DNA is tissue-specific. So is the location. In each tissue, the location of mCs is nonrandom, consisting of three clusters of heavily methylated regions, each of about 200 bases. However, the extent of methylation within each cluster is tissue-specific. The mCs are located entirely in C-G doublets and primarily in palindromic sequences, C-C-G-G sequences (10 methylatable sites) are almost completely methylated in all tissues examined, but T-G-G-A sequences (16 methylated in all tissues examined, but T-G-G-A sequences (16 metylatable sites) are methylated to different extents in each tissue. Neither the tissue specificity of methylation nor the clustering pattern is detectable by examining only G-C-G-G sites, leading us to emphasize the importance of total sequence determination for genomic DNAs in studies of methylation. The clustering pattern, which is preserved despite a 2-fold difference in mC content between brain and thymus, may indicate a role for DNA methylation in chromatin structure.[1]References
- Tissue specificity and clustering of methylated cystosines in bovine satellite I DNA. Sano, H., Sager, R. Proc. Natl. Acad. Sci. U.S.A. (1982) [Pubmed]
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