Nucleosomes containing the histone variant H2A.Bbd organize only 118 base pairs of DNA.
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.
Bao
Yunhe
Y
Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870, USA.
Konesky
Kasey
K
Park
Young-Jun
YJ
Rosu
Simona
S
Dyer
Pamela N
PN
Rangasamy
Danny
D
Tremethick
David J
DJ
Laybourn
Paul J
PJ
Luger
Karolin
K
D000595:Amino Acid Sequence; D000818:Animals; D020029:Base Pairing; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006657:Histones / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D008836:Micrococcal Nuclease / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009707:Nucleosomes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D016415:Sequence Alignment; D014158:Transcription, Genetic / Q000235:genetics
D006657:Histones; D009707:Nucleosomes; D004247:DNA; D008836:Micrococcal Nuclease