WDR5 is a core component of SET1-family complexes that achieve transcriptional activation via methylation of histone H3 on Nζ of Lys4 (H3K4). The role of WDR5 in the MLL1 complex has recently been described as specific recognition of dimethyl-K4 in the context of a histone H3 amino terminus; WDR5 is essential for vertebrate development, Hox gene activation and global H3K4 trimethylation. We report the high-resolution X-ray structures of WDR5 in the unliganded form and complexed with histone H3 peptides having unmodified and mono-, di-and trimethylated K4, which together provide the first comprehensive analysis of methylated histone recognition by the ubiquitous WD40-repeat fold. Contrary to predictions, the structures reveal that WDR5 does not read out the methylation state of K4 directly, but instead serves to present the K4 side chain for further methylation by SET1-family complexes.Reprints and permissions information is available online at http://npg.nature.com/reprintsandpermissions/ Correspondence should be addressed to G.L.V. (verdine@chemistry.harvard.edu).. AUTHOR CONTRIBUTIONS A.J.R. is responsible for the X-ray studies of the apo structure and the H3K4me1, H3K4me2 and H3K4me3 structures, W.-K.W. and H.L. are responsible for the unmodified peptide structure and an additional H3K4me2 structure (complex II), and D.M.G. performed the binding studies with some assistance from A.J.R. and W.-K.W. G.L.V., D.J.P. and C.D.A. supervised the structural and biochemical aspects of the project and take overall responsibility for their joint research. All authors discussed the results and commented on the manuscript. Accession codes. Protein Data Bank: coordinates have been deposited with the accession codes 2H68, 2CO0, 2H6K, 2H6N, 2CNX and 2H6Q, representing the apo structure, unmodified H3 complex, H3K4me1 complex, H3K4me2 complex crystal form I, H3K4me2 complex crystal form II and H3K4me3 complex, respectively. COMPETING INTERESTS STATEMENTThe authors declare that they have no competing financial interests.Supplementary information is available on the Nature Structural & Molecular Biology website. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptThe structure and dynamics of chromatin are increasingly recognized to be essential for mediating both global and local regulation of the genome 1,2 . Vital to maintaining and remodeling the various chromatin states are a collection of post-translational modifications of histones that are introduced in a highly regulated fashion and cause specific functional consequences 3 . In particular, post-translational introduction of methyl groups onto lysine side chains of histone proteins greatly affects chromatin function in complex and often opposing ways, resulting in either transcriptional repression or activation, contingent upon the precise location and degree of methylation [4][5][6][7] . For example, trimethylation of histone H3 at K9 or K27 is implicated in silencing of the underlying DNA 6,8 , whereas methylation at other s...

DNA gyrase is unique among type II topoisomerases in that its DNA supercoiling activity is unidirectional. The C-terminal domain of the gyrase A subunit (GyrA-CTD) is required for this supercoiling bias. We report here the x-ray structure of the Escherichia coli GyrA-CTD (Protein Data Bank code 1ZI0). The E. coli GyrA-CTD adopts a circular-shaped ␤-pinwheel fold first seen in the Borrelia burgdorferi GyrA-CTD. However, whereas the B. burgdorferi GyrA-CTD is flat, the E. coli GyrA-CTD is spiral. DNA relaxation assays reveal that the E. coli GyrA-CTD wraps DNA inducing substantial (؉) superhelicity, while the B. burgdorferi GyrA-CTD introduces a more modest (؉) superhelicity. The observation of a superhelical spiral in the present structure and that of the Bacillus stearothermophilus ParC-CTD structure suggests unexpected similarities in substrate selectivity between gyrase and Topo IV enzymes. We propose a model wherein the right-handed ((؉) solenoidal) wrapping of DNA around the E. coli GyrA-CTD enforces unidirectional (؊) DNA supercoiling.

A nickel(II)-PNA bioconjugate was prepared by formation of a salicylaldimine complex with the amino terminus of a peptide-PNA hybrid with the sequence Arg-His-Gly-[TACCTAGCAT]PNA-Arg-CONH2. Hybridization to complementary oligodeoxynucleotides was demonstrated, and covalent adduct formation was observed upon addition of KHSO5 as oxidant. In the absence of PNA, the reactivity of the phenolic radical generated as an intermediate was found to be G >> T >> C, A; by inclusion of the PNA delivery agent, cross-links between the two oligomers could be observed with T and C bases in the vicinity of the nickel complex, although G was still the most reactive site. The metal complex could be removed by treatment with EDTA following which the Schiff base linkage was readily hydrolyzed. The final result in this case is a salicylaldehyde moiety appended at the target site in DNA.

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