title: HP1β-dependent recruitment of UBF1 to irradiated chromatin occurs simultaneously with CPDs.
abstract: BACKGROUND
  The repair of spontaneous and induced DNA lesions is a multistep process. Depending on the type of injury, damaged DNA is recognized by many proteins specifically involved in distinct DNA repair pathways.
  
  
  RESULTS
  We analyzed the DNA-damage response after ultraviolet A (UVA) and γ irradiation of mouse embryonic fibroblasts and focused on upstream binding factor 1 (UBF1), a key protein in the regulation of ribosomal gene transcription. We found that UBF1, but not nucleolar proteins RPA194, TCOF, or fibrillarin, was recruited to UVA-irradiated chromatin concurrently with an increase in heterochromatin protein 1β (HP1β) level. Moreover, Förster Resonance Energy Transfer (FRET) confirmed interaction between UBF1 and HP1β that was dependent on a functional chromo shadow domain of HP1β. Thus, overexpression of HP1β with a deleted chromo shadow domain had a dominant-negative effect on UBF1 recruitment to UVA-damaged chromatin. Transcription factor UBF1 also interacted directly with DNA inside the nucleolus but no interaction of UBF1 and DNA was confirmed outside the nucleolus, where UBF1 recruitment to DNA lesions appeared simultaneously with cyclobutane pyrimidine dimers; this occurrence was cell-cycle-independent.
  
  
  CONCLUSIONS
  We propose that the simultaneous presence and interaction of UBF1 and HP1β at DNA lesions is activated by the presence of cyclobutane pyrimidine dimers and mediated by the chromo shadow domain of HP1β. This might have functional significance for nucleotide excision repair.
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Stixová
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: Petra
authors.initials: P
authors.lastname: Sehnalová
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: Soňa
authors.initials: S
authors.lastname: Legartová
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: Jana
authors.initials: J
authors.lastname: Suchánková
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: Tereza
authors.initials: T
authors.lastname: Hrušková
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Kozubek
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic ; Faculty of Informatics, Masaryk University, Botanická 68a, 602 00 Brno, Czech Republic.
authors.forename: Dmitry V
authors.initials: DV
authors.lastname: Sorokin
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic ; Faculty of Informatics, Masaryk University, Botanická 68a, 602 00 Brno, Czech Republic.
authors.forename: Pavel
authors.initials: P
authors.lastname: Matula
authors.affiliation: Institute of Cellular Biology and Pathology, the First Faculty of Medicine, Charles University in Prague, Albertov 4, 128 01 Prague, Czech Republic.
authors.forename: Ivan
authors.initials: I
authors.lastname: Raška
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: Aleš
authors.initials: A
authors.lastname: Kovařík
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Fulneček
authors.affiliation: Academy of Sciences of the Czech Republic, Institute of Biophysics, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: Eva
authors.initials: E
authors.lastname: Bártová
keywords: DNA repair; DNA-damage response; Irradiation; Live-cell studies; Nucleolus; UBF1