tailieunhanh - Báo cáo Y học: Dnmt3a and Dnmt1 functionally cooperate during de novo methylation of DNA

Dnmt3a is ade novoDNA methyltransferase that modifies unmethylated DNA. In contrast Dnmt1 shows high pre-ference for hemimethylatedDNA. However, Dnmt1 can be activated for themethylationof show here that the Dnmt3a andDnmt1 DNA methyltransferases functionally cooperate in de novo methylation of DNA, because a fivefold stimulation of methylation activity is observed if both enzymes are present. | Eur. J. Biochem. 269 4981-4984 2002 FEBS 2002 doi Dnmt3a and Dnmtl functionally cooperate during de novo methylation of DNA Mehrnaz Fatemi Andrea Hermann Humaira Gowher and Albert Jeltsch Institut fur Biochemie Justus-Liebig-Universitat Giefien Germany Dnmt3a is a de novo DNA methyltransferase that modifies unmethylated DNA. In contrast Dnmt1 shows high preference for hemimethylated DNA. However Dnmt1 can be activated for the methylation of unmodified DNA. We show here that the Dnmt3a and Dnmt1 DNA methyltransferases functionally cooperate in de novo methylation of DNA because a fivefold stimulation of methylation activity is observed if both enzymes are present. Stimulation is observed if Dnmt3a is used before Dnmt1 but not if incubation with Dnmt1 precedes Dnmt3a demonstrating that methylation of the DNA by Dnmt3a stimulates Dnmt1 and that no physical interaction of Dnmt1 and Dnmt3a is required. If Dnmt1 and Dnmt3a were incubated together a slightly increased stimulation is observed that could be due to a direct interaction of these enzymes. In addition we show that Dnmt1 is stimulated for methylation of unmodified DNA if the DNA already carries some methyl groups. We conclude that after initiation of de novo methylation of DNA by Dnmt3a Dnmt1 becomes activated by the pre-existing methyl groups and further methylates the DNA. Our data suggest that Dnmt1 also has a role in de novo methylation of DNA. This model agrees with the biochemical properties of these enzymes and provides a mechanistic basis for the functional cooperation of different DNA MTases in de novo methylation of DNA that has also been observed in vivo. Keywords DNA methylation enzyme mechanism DNA methyltransferase Dnmt1 Dnmt3a. Cytosine residues are methylated at the 5-position for 70-80 of all CG sequences in mammalian DNA. The pattern of DNA methylation serves as an epigenetic mark in general leading to a repression of gene expression reviews 1 2 3 . It is used .

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