Upstream binding factor association induces large-scale chromatin decondensation.
The function of upstream binding factor (UBF), an essential component of the RNA polymerase (pol) I preinitiation complex, is unclear. Recently, UBF was found distributed throughout ribosomal gene repeats rather than being restricted to promoter regions. This observation has led to the speculation that one role of UBF binding may be to induce chromatin remodeling. To directly evaluate the impact of UBF on chromatin structure, we used an in vivo assay in which UBF is targeted via a lac repressor fusion protein to a heterochromatic, amplified chromosome region containing lac operator repeats. We show that the association of UBF with this locus induces large-scale chromatin decondensation. This process does not appear to involve common remodeling complexes, including SWI/SNF and histone acetyltransferases, and is independent of histone H3 lysine 9 acetylation. However, UBF recruits the pol I-specific, TATA box-binding protein containing complex SL1 and pol I subunits. Our results suggest a working hypothesis in which the dynamic association of UBF with ribosomal DNA clusters recruits the pol I transcription machinery and maintains these loci in a transcriptionally competent configuration. These studies also provide an in vivo model simulating ribosomal DNA transactivation outside the nucleolus, allowing temporal and spatial analyses of chromatin remodeling and assembly of the pol I transcription machinery.
Chen
Danyang
D
Department of Cell and Molecular Biology, The Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
Belmont
Andrew S
AS
Huang
Sui
S
D000107:Acetylation; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002843:Chromatin / Q000378:metabolism*; D042002:Chromatin Assembly and Disassembly / Q000502:physiology*; D006224:Cricetinae; D004247:DNA / Q000235:genetics; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D007763:Lac Operon; D035463:Pol1 Transcription Initiation Complex Proteins / Q000235:genetics / Q000378:metabolism*; D012318:RNA Polymerase I / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism
D002843:Chromatin; D006657:Histones; D035463:Pol1 Transcription Initiation Complex Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; C063844:transcription factor UBF; D004247:DNA; D012318:RNA Polymerase I