The Repressor MDBP-2 is a Member of the Histone H1 Family That Binds Preferentially in vitro and in vivo to Methylated Nonspecific DNA Sequences

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 89; no. 20; pp. 9499 - 9503
• Main Authors: Jost, Jean-Pierre, Hofsteenge, Jan
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 15.10.1992; National Acad Sciences; National Academy of Sciences
• Subjects: 5-Methylcytosine; Amino Acid Sequence; Animals; Antibodies; Base Sequence; Biochemistry; Cellular biology; Chickens; Cytosine - analogs & derivatives; Cytosine - metabolism; Deoxyribonucleic acid; DNA; DNA-Binding Proteins - metabolism; Gels; Gene Expression Regulation; Heterochromatin; Histones; Histones - chemistry; Liver; Macromolecular Substances; Methylation; Molecular Sequence Data; Molecular Weight; Nuclear Proteins - metabolism; Oligodeoxyribonucleotides - chemistry; Oligonucleotides; Proteins; Repressor Proteins - metabolism; Structure-Activity Relationship; Vitellogenins - genetics
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.89.20.9499

MDBP-2 is a repressor that binds preferentially to methylated DNA. Peptides derived from MDBP-2 were sequenced. The sequences of the two peptides, KPAGPSVTELITK and ALAAGGYDVEK, are identical to those found in the chicken histone H1 core protein. In SDS/polyacrylamide gels MDBP-2 has an apparent molecular mass of 21 kDa, and antibodies directed against calf thymus total histone H1 cross-react with MDBP-2. The preferential binding of affinity-purified MDBP-2 to methylated DNA is not sequence-specific but requires a minimum length of 30 base pairs and one pair of symmetrically methylated (i.e., methylated on both strands) CpG dinucleotides. As previously shown, there is a decrease in the binding activity of MDBP-2 to methylated DNA upon estradiol treatment. Immunoblots show that upon estradiol treatment the amount of immunocrossreacting MDBP-2 protein remains unchanged. MDBP-2 enables another protein to bind DNA which by itself does not bind methylated DNA. Ultraviolet crosslinking and selective immunoadsorption assays with anti-histone H1 antibodies show that in vivo MDBP-2 preferentially binds to the methylated repressed vitellogenin gene. It is concluded that MDBP-2 may participate in the long-term silencing of genes (formation of heterochromatin) through selective binding to methylated DNA.