Specificity of Dnmt1 for Methylation of Hemimethylated CpG Sites Resides in Its Catalytic Domain

SummaryThe maintenance methylation of hemimethylated CpG sites by the DNA methyltransferase Dnmt1 is the molecular basis of the inheritance of DNA methylation patterns. Based on structural data and kinetics obtained with a truncated form of Dnmt1, an autoinhibition model for the specificity of Dnmt1 was proposed in which unmethylated DNA binds to Dnmt1's CXXC domain, which prevents its methylation. We have prepared CXXC domain variants that lost DNA binding. Corresponding full-length Dnmt1 variants did not display a reduction in specificity, indicating that the autoinhibition model does not apply in full-length Dnmt1. Furthermore, we show that the Dnmt1 M1235S variant, which carries an exchange in the catalytic domain of the enzyme, has a marked reduction in specificity, indicating that the recognition of the hemimethylated state of target sites resides within the catalytic domain.

Graphical AbstractFigure optionsDownload high-quality image (161 K)Download as PowerPoint slideHighlights
► DNA methylation is inherited by specific methylation of hemimethylated CpG sites by Dnmt1
► Loss of DNA binding to the CXXC domain did not weaken the specificity of Dnmt1
► A mutation in the catalytic domain caused a strong reduction in Dnmt1's specificity
► Recognition of the hemimethylated CpG resides within the catalytic domain of Dnmt1