Cross-talk between DNA methylation and histone post-translational modifications in Arabidopsis
EMSL Project ID
44640
Abstract
In eukaryotes, chromosomal DNA must be highly compacted by proteins in order to fit within the confines of the nucleus, yet must also allow the DNA to be accessible for transcription, replication and repair. DNA-protein complexes are collectively known as chromatin. The fundamental unit of chromatin is the nucleosome core particle, a structure in which ~147 bp of DNA is wrapped, nearly twice, around an octamer of the core histone proteins H2A, H2B, H3 and H4 (two molecules of each). The linker region between adjacent core particles, averaging ~50 basepairs, can be bound by so-called linker histones (e.g. Histone H1), allowing higher-order packing of the chromatin into a more condensed form. Core and linker histones can be post-translationally modified in various ways, including acetylation, methylation, phosphorylation, sumoylation and ubiquitination. Depending on the context of the modifications, positive or negative effects on expression of the associated genes are mediated by these post-translational modifications. In parallel with the histone modifications, the DNA can be modified by the methylation of cytosines, which typically mediates gene silencing if promoter regions are hypermethylated. Genetic and biochemical evidence suggests that there is crosstalk between histone modifications and cytosine methylation, however the spectrum of histone modifications that correlate with, or are specified by, different patterns of cytosine methylation are unclear. To address this question, we are collaborating with Ljiljana Pasa-Tolic's team at EMSL, using state-of-the-art mass spectrometry techniques to analyze histones that have been purified from Arabidopsis thaliana plants that are defective for specific enzymes of the DNA methylation machinery. Our goal is to define the suites of histone post-translational modifications that correlate with different patterns of cytosine methylation. These patterns include methylation occurring at CG and CNG motifs, which is accomplished by the cytosine methyltransferases MET1 and CMT3 and can be maintained following each round of replication. In addition, de novo methylation of cytosines in any sequence context can be accomplished by DRM2 in a process directed by 24 nt RNAs. Preliminary evidence indicates that altered histone profiles occur in met1 mutants, and new instrumentation and approaches developed at EMSL are now in place to complete the analyses. These studies should be readily publishable and fit with the 'Biological interactions and dynamics' science theme call as well as the mission of the EMSL to leverage its unique expertise for the analysis of complex problems beyond the capabilities of individual academic laboratories.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2011-10-01
End Date
2012-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Ream TS, JR Haag, F Pontvianne, CD Nicora, AD Norbeck, L Pasa-Tolic, and CS Pikaard. 2015. "Subunit compositions of Arabidopsis RNA polymerases I and III reveal Pol I- and Pol III- specific forms of the AC40 subunit, and alternative C53 subunits ." Nucleic Acids Research 43(8):4163-4178. doi:10.1093/nar/gkv247