Structural Biology of DNA Methylation Maintenance

[DNA methylation]
Arita Lab is focusing on molecular mechanism of DNA methylation maintenance. In mammal, DNA methylation occurs at 5th position of cytosine in CpG sequence. DNA methylation is known to determine the gene expression pattern in differentiated cells. To maintain the cell phenotype, DNA methylation pattern is inherited after each replication and cell division. Abnormal DNA methylation, such as hypermethylation of tumor suppressor genes and hypomethylation of retrotransposons and centromere region, is involved in tumorigenesis. Thus, faithful inheritance of DNA methylation pattern is important for the normal cell growth.

[DNA methylation maintenance]
Two proteins are essential for DNA methylation maintenance: maintenance DNA methyltransferase DNMT1 and ubiquitin E3-ligase UHRF1. The current model of DNA methylation maintenance is as follows:
After DNA replication, hemi-methylation site is recognized by UHRF1 SRA domain. Histone H3 N-terminal tail, K14, K18 and K23 undergoes mono-ubiquitination by UHRF1. The ubiquitinated histone H3 recruits DNMT1 to the methylation sites, and finally DNMT1 methylates nascent strand. Recently, we found that replication factors that associate with PCNA are involved in DNA methylation maintenance. Methylated DNA ligase1 and ubiquitinated PAF15 recruit UHRF1 and DNMT1 to DNA replication sites, respectively.

For comprehensive understanding of DNA methylation maintenance, we use structural biology techniques, X-ray crystallography, SAXS, NMR, HS-AFM and Cryo-EM.