Nucleosomes containing the histone variant H2A.Bbd organize only 118 base pairs of DNA

• Autores: Yunhe Bao, Kasey Konesky, Young-Jun Park, Pamela N. Dyer, Danny Rangasamy, David J. Tremethick, Karolin Luger
• Localización: EMBO journal: European Molecular Biology Organization, ISSN 0261-4189, Nº. 16, 2004, págs. 3314-3324
• Idioma: inglés
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• Resumen

  • H2A.Bbd is an unusual histone variant whose sequence is only 48% conserved compared to major H2A. The major sequence differences are in the docking domain that tethers the H2A–H2B dimer to the (H3–H4)2 tetramer; in addition, the C-terminal tail is absent in H2A.Bbd. We assembled nucleosomes in which H2A is replaced by H2A.Bbd (Bbd-NCP), and found that Bbd-NCP had a more relaxed structure in which only 118±2 bp of DNA is protected against digestion with micrococcal nuclease. The absence of fluorescence resonance energy transfer between the ends of the DNA in Bbd-NCP indicates that the distance between the DNA ends is increased significantly. The Bbd docking domain is largely responsible for this behavior, as shown by domain-swap experiments. Bbd-containing nucleosomal arrays repress transcription from a natural promoter, and this repression can be alleviated by transcriptional activators Tax and CREB. The structural properties of Bbd-NCP described here have important implications for the in vivo function of this histone variant and are consistent with its proposed role in transcriptionally active chromatin.