3544 Nucleic Acids Research, 2010, Vol. 38, No. 11 Histone H1 and global gene silencing Transcription of multiple genes was aﬀected in H1 12/ 12+ﬂox and H1 12/12 #1 cells. However, the main change was decrease in transcription, suggesting that H1 is involved in transcriptional activation, rather than in global transcriptional repression. Further, individual H1 variant knockdown in human cell lines also suggests that histone H1 generally activates gene expression (18). Further characterization of the established DT40 cells expressing diﬀerent single H1 variants may clarify the involvement of individual H1 histones in transcriptional regulation. SUPPLEMENTARY DATA Supplementary Data are available at NAR Online. ACKNOWLEDGEMENTS We thank Xing Zhang and Xiaodong Cheng (Emory University) for critical reading of manuscript, Yoko Hayashi-Takanaka (Osaka University) for technical assis- tance. Michael Reth (Max-Planck Institute) and Hitoshi Niwa (RIKEN) kindly provided the Mer-Cre-Mer expres- sion vector and the pCAG-IRES-puro expression vector, respectively. We also thank Toshiyuki Matsui (Kyoto University) for the statistical evaluation. FUNDING A grant-in-aids from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan (to Y.S., Y.T., H.K. and M.T.). Funding for open access charge: MEXT of Japan. Conﬂict of interest statement. None declared. REFERENCES 1. Luger,K., Mader,A.W., Richmond,R.K., Sargent,D.F. and Richmond,T.J. (1997) Crystal structure of the nucleosome core particle at 2.8 A resolution. Nature, 389, 251–260. 2. Davey,C.A., Sargent,D.F., Luger,K., Maeder,A.W. and Richmond,T.J. (2002) Solvent mediated interactions in the structure of the nucleosome core particle at 1.9 a resolution. J. Mol. Biol., 319, 1097–1113. 3. Ramakrishnan,V., Finch,J.T., Graziano,V., Lee,P.L. and Sweet,R.M. 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