Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.31.1 (micrococcal nuclease)
 2,818 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nuclease hypersensitive sites exist in vivo in the chromatin of the integrated human immunodeficiency virus (HIV)-1 proviral genome, in the 5'-long terminal repeat (LTR) within the promoter/enhancer region near Sp1 and NFkappaB binding sites. Previous studies from the Kadonaga and Jones laboratories have shown that Sp1 and NFkappaB can establish hypersensitive sites in a truncated form of this LTR when added before in vitro chromatin assembly with Drosophila extracts, thus facilitating subsequent transcriptional activation of a linked reporter gene upon the association of additional factors (Pazin, M. J., Sheridan, P. L., Cannon, K., Cao, Z., Keck, J. G., Kadanaga, J. T., and Jones, K. A. (1996) Genes & Dev. 10, 37-49). Here we assess the role of a full-length LTR and 1 kilobase pair of downstream flanking HIV sequences in chromatin remodeling when these transcription factors are added after chromatin assembly. Using Xenopus laevis oocyte extracts to assemble chromatin in vitro, we have confirmed that Sp1 and NFkappaB can indeed induce sites hypersensitive to DNase I, micrococcal nuclease, or restriction enzymes on either side of factor binding sites in chromatin but not naked DNA. We extend these earlier studies by demonstrating that the process is ATP-dependent when the factors are added after chromatin assembly and that histone H1, AP1, TBP, or Tat had no effect on hypersensitive site formation. Furthermore, we have found that nucleosomes upstream of NFkappaB sites are rotationally positioned prior to factor binding and that their translational frame is registered after binding NFkappaB. On the other hand, binding of Sp1 positions adjacent downstream nucleosome(s). We term this polar repositioning because each factor aligns nucleosomes only on one side of its binding sites. Mutational analysis and oligonucleotide competition each demonstrated that this remodeling required Sp1 and NFkappaB binding sites.
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PMID:In vitro chromatin assembly of the HIV-1 promoter. ATP-dependent polar repositioning of nucleosomes by Sp1 and NFkappaB. 921 15

The Saccharomyces cerevisiae CHA1 gene encodes the catabolic L-serine (L-threonine) dehydratase. We have previously shown that the transcriptional activator protein Cha4p mediates serine/threonine induction of CHA1 expression. We used accessibility to micrococcal nuclease and DNase I to determine the in vivo chromatin structure of the CHA1 chromosomal locus, both in the non-induced state and upon induction. Upon activation, a precisely positioned nucleosome (nuc-1) occluding the TATA box and the transcription start site is removed. A strain devoid of Cha4p showed no chromatin alteration under inducing conditions. Five yeast TBP mutants defective in different steps in activated transcription abolished CHA1 expression, but failed to affect induction-dependent chromatin rearrangement of the promoter region. Progressive truncations of the RNA polymerase II C-terminal domain caused a progressive reduction in CHA1 transcription, but no difference in chromatin remodeling. Analysis of swi1, swi3, snf5 and snf6, as well as gcn5, ada2 and ada3 mutants, suggested that neither the SWI/SNF complex nor the ADA/GCN5 complex is involved in efficient activation and/or remodeling of the CHA1 promoter. Interestingly, in a sir4 deletion strain, repression of CHA1 is partly lost and activator-independent remodeling of nuc-1 is observed. We propose a model for CHA1 activation based on promoter remodeling through interactions of Cha4p with chromatin components other than basal factors and associated proteins.
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PMID:Nucleosome structure of the yeast CHA1 promoter: analysis of activation-dependent chromatin remodeling of an RNA-polymerase-II-transcribed gene in TBP and RNA pol II mutants defective in vivo in response to acidic activators. 977 46