The distinct contributions of histone tails and their acetylation to nucleosomal stability were examined by mechanical disruption of individual nucleosomes in a single chromatin fiber using an optical trap. Enzymatic removal of H2A/H2B tails primarily decreased the strength of histone-DNA interactions located ∼±36 bp from the dyad axis of symmetry (off-dyad strong interactions), whereas removal of the H3/H4 tails played a greater role in regulating the total amount of DNA bound. Similarly, nucleosomes composed of histones acetylated to different degrees by the histone acetyltransferase p300 exhibited significant decreases in the off-dyad strong interactions and the total amount of DNA bound. Acetylation of H2A/H2B appears to play a particularly critical role in weakening the off-dyad strong interactions. Collectively, our results suggest that the destabilizing effects of tail acetylation may be due to elimination of specific key interactions in the nucleosome.
Bibliographical noteFunding Information:
We are grateful to Dr Karen Adelman for stimulating scientific conversation, critical advice and comments at all stages of the work. We thank Jennifer Smith, Mi Young Kim and Chad Simmons for excellent technical assistance, and Dr Alla Shundrovsky, Dr Steve Koch, and Richard Yeh for instrument fabrication, software design, and help with data analysis. We also thank Dr Craig L. Peterson for the pCP681 plasmid. M.D.W. is supported by grants from the NIH, the Beckman Young Investigator Award, the Alfred P. Sloan Research Fellow Award, and the Keck Foundation's Distinguished Young Scholar Award. W.L.K. is supported by grants from the NIH and the American Cancer Society. J.T.L. is supported by a grant from the NIH GM 25232. D.A.W is also supported by Cornell University Molecular Biophysics Training Grant from NIH.
- histone tails
- optical trapping
- single molecule