title: Revisiting chromatin binding of the Arabidopsis UV-B photoreceptor UVR8.
abstract: BACKGROUND
  Plants perceive UV-B through the UV RESISTANCE LOCUS 8 (UVR8) photoreceptor and UVR8 activation leads to changes in gene expression such as those associated with UV-B acclimation and stress tolerance. Albeit functionally unrelated, UVR8 shows some homology with RCC1 (Regulator of Chromatin Condensation 1) proteins from non-plant organisms at the sequence level. These proteins act as guanine nucleotide exchange factors for Ran GTPases and bind chromatin via histones. Subsequent to the revelation of this sequence homology, evidence was presented showing that UVR8 activity involves interaction with chromatin at the loci of some target genes through histone binding. This suggested a UVR8 mode-of-action intimately and directly linked with gene transcription. However, several aspects of UVR8 chromatin association remained undefined, namely the impact of UV-B on the process and how UVR8 chromatin association related to the transcription factor ELONGATED HYPOCOTYL 5 (HY5), which is important for UV-B signalling and has overlapping chromatin targets. Therefore, we have investigated UVR8 chromatin association in further detail.
  
  
  RESULTS
  Unlike the claims of previous studies, our chromatin immunoprecipitation (ChIP) experiments do not confirm UVR8 chromatin association. In contrast to human RCC1, recombinant UVR8 also does not bind nucleosomes in vitro. Moreover, fusion of a VP16 activation domain to UVR8 did not alter expression of proposed UVR8 target genes in transient gene expression assays. Finally, comparison of the Drosophila DmRCC1 and the Arabidopsis UVR8 crystal structures revealed that critical histone- and DNA-interaction residues apparent in DmRCC1 are not conserved in UVR8.
  
  
  CONCLUSIONS
  This has led us to conclude that the cellular activity of UVR8 likely does not involve its specific binding to chromatin at target genes.
authors: Department of Botany and Plant Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. melanie.binkert@unige.ch.
authors: Melanie
authors: M
authors: Binkert
authors: Department of Botany and Plant Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. carlos.crocco@unige.ch.
authors: Carlos D
authors: CD
authors: Crocco
authors: Department of Molecular Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. babatunde.ekundayo@unige.ch.
authors: Babatunde
authors: B
authors: Ekundayo
authors: Department of Botany and Plant Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. kelvin.lau@unige.ch.
authors: Kelvin
authors: K
authors: Lau
authors: Department of Botany and Plant Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. sarah.raffelberg@unige.ch.
authors: Sarah
authors: S
authors: Raffelberg
authors: Department of Botany and Plant Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. kimberley.tilbrook@csiro.au.|Present Address: CSIRO Agriculture, Canberra, Australia. kimberley.tilbrook@csiro.au.
authors: Kimberley
authors: K
authors: Tilbrook
authors: Department of Botany and Plant Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. ruohe.yin@unige.ch.
authors: Ruohe
authors: R
authors: Yin
authors: Department of Botany and Plant Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. richard.chappuis@unige.ch.
authors: Richard
authors: R
authors: Chappuis
authors: Department of Molecular Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. thomas.schalch@unige.ch.|Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, CH-1211, Geneva 4, Switzerland. thomas.schalch@unige.ch.
authors: Thomas
authors: T
authors: Schalch
authors: Department of Botany and Plant Biology, University of Geneva, Sciences III, 30 Quai E. Ansermet, CH-1211, Geneva 4, Switzerland. roman.ulm@unige.ch.|Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, CH-1211, Geneva 4, Switzerland. roman.ulm@unige.ch.
authors: Roman
authors: R
authors: Ulm
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002843:Chromatin / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D017343:Genes, Plant; D055519:Photoreceptors, Plant / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding
chemical_list: D029681:Arabidopsis Proteins; D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D055519:Photoreceptors, Plant; C525052:Uvr8 protein, Arabidopsis