title: Inducible DNA demethylation mediated by the maize Suppressor-mutator transposon-encoded TnpA protein.
abstract: Heritable epigenetic inactivation of the maize Suppressor-mutator (Spm) transposon is associated with promoter methylation, and its reversal is mediated by the transposon-encoded TnpA protein. We have developed an assay that permits demethylation of the Spm sequence to be controlled by inducing the expression of TnpA in plant cells. Using this assay, we show that demethylation is a rapid, active process. TnpA is a weak transcriptional activator, and deletions that abolish its transcriptional activity also eliminate its demethylation activity. We show that cell cycle and DNA synthesis inhibitors interfere with TnpA-mediated Spm demethylation. We further show that TnpA has a much lower affinity for fully methylated than for hemimethylated or unmethylated DNA fragments derived from Spm termini. Based on these observations, we suggest that TnpA binds to the postreplicative, hemimethylated Spm sequence and promotes demethylation either by creating an appropriate demethylation substrate or by itself participating in or recruiting a demethylase.
authors.affiliation: Biology Department, Life Sciences Consortium and Plant Physiology Program, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Hongchang
authors.initials: H
authors.lastname: Cui
authors.forename: Nina V
authors.initials: NV
authors.lastname: Fedoroff
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology; D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D016590:Aphidicolin / Q000494:pharmacology; D001593:Benzyl Compounds; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D046508:Culture Techniques; D019175:DNA Methylation; D004261:DNA Replication / Q000187:drug effects; D018744:DNA, Plant / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D005786:Gene Expression Regulation; D007701:Kinetin; D009280:Naphthaleneacetic Acids / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics; D030821:Plants, Genetically Modified; D011687:Purines / Q000494:pharmacology; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D013489:Suppression, Genetic / Q000235:genetics*; D014026:Nicotiana / Q000235:genetics / Q000254:growth & development; D015533:Transcriptional Activation / Q000235:genetics; D003313:Zea mays / Q000235:genetics*
chemical_list: D001593:Benzyl Compounds; D018744:DNA, Plant; D004268:DNA-Binding Proteins; D009280:Naphthaleneacetic Acids; D010940:Plant Proteins; D011687:Purines; D012097:Repressor Proteins; D015084:2,4-Dichlorophenoxyacetic Acid; D016590:Aphidicolin; C090046:olomoucine; D003907:Dexamethasone; D001973:Bromodeoxyuridine; D000225:Adenine; C480551:benzylaminopurine; D007701:Kinetin