title: Cleavage of a model DNA replication fork by a methyl-specific endonuclease.
abstract: Epigenetic DNA methylation is involved in many biological processes. An epigenetic status can be altered by gain or loss of a DNA methyltransferase gene or its activity. Repair of DNA damage can also remove DNA methylation. In response to such alterations, DNA endonucleases that sense DNA methylation can act and may cause cell death. Here, we explored the possibility that McrBC, a methylation-dependent DNase of Escherichia coli, cleaves DNA at a replication fork. First, we found that in vivo restriction by McrBC of bacteriophage carrying a foreign DNA methyltransferase gene is increased in the absence of homologous recombination. This suggests that some cleavage events are repaired by recombination and must take place during or after replication. Next, we demonstrated that the enzyme can cleave a model DNA replication fork in vitro. Cleavage of a fork required methylation on both arms and removed one, the other or both of the arms. Most cleavage events removed the methylated sites from the fork. This result suggests that acquisition of even rarely occurring modification patterns will be recognized and rejected efficiently by modification-dependent restriction systems that recognize two sites. This process might serve to maintain an epigenetic status along the genome through programmed cell death.
authors: Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, Shirokanedai, Tokyo 108-8639, Japan.
authors: Ken
authors: K
authors: Ishikawa
authors: Naofumi
authors: N
authors: Handa
authors: Lauren
authors: L
authors: Sears
authors: Elisabeth A
authors: EA
authors: Raleigh
authors: Ichizo
authors: I
authors: Kobayashi
mesh_terms: D053837:DNA Cleavage; D019175:DNA Methylation; D004261:DNA Replication; D004262:DNA Restriction Enzymes / Q000378:metabolism*; D044127:Epigenesis, Genetic; D008957:Models, Genetic
chemical_list: D004262:DNA Restriction Enzymes; C120301:McrBC endonuclease