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Molecular and Cellular Biology, February 2001, p. 1155-1163, Vol. 21, No. 4
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.4.1155-1163.2001

Acetylation of a Specific Promoter Nucleosome Accompanies Activation of the epsilon -Globin Gene by beta -Globin Locus Control Region HS2

Chang-Yun Gui and Ann Dean*

Laboratory of Cellular and Developmental Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-2715

Received 4 October 2000/Returned for modification 20 November 2000/Accepted 28 November 2000

On stably replicating episomes, transcriptional activation of the varepsilon -globin promoter by the beta -globin locus control region HS2 enhancer is correlated with an increase in nuclease sensitivity which is limited to the TATA-proximal nucleosome (N1). To elucidate what underlies this increase in nuclease sensitivity and the link between chromatin modification and gene expression, we examined the nucleoprotein composition and histone acetylation status of transcriptionally active and inactive promoters. Micrococcal nuclease digestion of active promoters in nuclei released few nucleosome-like nucleoprotein complexes containing N1 sequences in comparison to results with inactive promoters. We also observed that N1 DNA fragments from active promoters are of a subnucleosomal length. Nevertheless, chromatin immunoprecipitation experiments indicate that histones H3 and H4 are present on N1 sequences from active promoters, with H3 being dramatically hyperacetylated compared with that from inactive promoters and vector sequences. Strikingly, H3 in the adjacent upstream nucleosome (N2) does not appear to be differentially acetylated in active and inactive promoters, indicating that the nucleosome modification of the promoter that accompanies transactivation by HS2 is highly directed and specific. However, global acetylation of histones in vivo by trichostatin A did not activate transcription in the absence of HS2, suggesting that HS2 contributes additional activities necessary for transactivation. N1 sequences from active promoters also contain reduced levels of linker histone H1. The detection of a protected subnucleosomal sized N1 DNA fragment and the recovery of N1 DNA sequences in immunoprecipitations using anti-acetylated H3 and H4 antibodies argue that N1 is present, but in an altered conformation, in the active promoters.

* Corresponding author. Mailing address: Laboratory of Cellular and Developmental Biology, NIDDK, NIH, Building 6, Room B1-08, 6 Center Dr., MSC 2715, Bethesda, MD 20892-2715. Phone: (301) 496-6068. Fax: (301) 496-5239. E-mail: anndean{at}helix.nih.gov.

Molecular and Cellular Biology, February 2001, p. 1155-1163, Vol. 21, No. 4
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.4.1155-1163.2001


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