The protein MeCP2 binds to symmetrically methylated CpG dinucleotides and is thought to transmit the (generally) repressive signals encoded in DNA methylation patterns. Mutations in MeCP2 lead to Rett syndrome. Here, MeCP2-DNA complexes have been imaged by AFM (Digital Instruments Nanoscope) in air using human MeCP2 and an 828 bp DNA sequence containing several methylated CpGs. MeCP2 molecules appear as bright particles in AFM images. Volume measurements of the complexes suggest that MeCP2 monomers (circular particles) and dimers (larger elliptical particles) are present and suggest that MeCP2 binds DNA cooperatively. Other images in the grouped set show looped structures and large complexes containing multiple DNA strands and MeCP2 molecules. These configurations are likely promoted by the multiple independent DNA-binding domains of MeCP2 and relevant to the in vivo interactions between MeCP2 and chromatin.
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