Purification of MeCP2-Containing Deacetylase from Xenopus laevis

DNA methylation has long been associated with stable transcriptional silencing and a repressive chromatin structure (review refs . 1 ,2 ). Differential methylation is associated with imprinting, carcinogenesis, silencing of repetitive DNA, and allows for differentiating cells to efficiently shut off unnecessary genes. In vertebrates, where 60–90% of genomic CpG dinucleotides are methylated, methylation-dependent repression is vital for proper embryonic development (3 ). Microinjection experiments using methylated DNA templates implicate chromatin structure as an underlying mechanism of methylation-dependent silencing (4 ,5 ). Methyl-specific transcriptional repression requires chromatin assembly, and can be partially relieved by the histone deacetylase inhibitor Trichostatin A. In addition, two proteins have been identified, MeCP1 (6 ) and MeCP2 (7 ), that specifically bind to methylated DNA and mediate transcriptional repression. MeCP1 is a relatively uncharacterized complex that requires at least 12 symmetrical methyl-CpGs for DNA binding (6 ). MeCP2 is a single polypeptide containing a methyl-binding domain capable of binding a single methyl-CpG, and a transcriptional repression domain (8 ). Recently MeCP2 was shown to interact with the Sin3 corepressor and histone deacetylase (9 ,10 ). Changes in the acetylation state of the core histone tails correlates with changes in transcription (reviewed in refs. 11 ,12 ), and several transcriptional repression complexes containing histone deacetylases have recently been described (9 ,13 ,14 )