(A) Primary structure of the X. laevis GH1.0 domain. Residues close to core or linker DNA are marked by blue (sense) or cyan (anti-sense) squares and triangles, respectively, coloured as in panel B. Post-translational modifications (PTMs) in mammalian histones H1.1-H1.5 (; ; ) are in green. (B) Summary of DNA-proximal residues. GH1.0 residues are shown next to the DNA phosphate group (in red) to which they are most proximal. Residues shown are within ~4 Å of the DNA, except for Ser29 which is ~5 Å away. Basic residues are in blue, other residues in violet. The six additional linker nucleotide positions contacted by the GH5 domain in the structure of () are indicated by a red dot. (C) Plot of sequence conservation versus distance from DNA for surface-exposed residues in the GH1.0 domain. For each residue, the distance from each stereochemically allowed rotamer to the closest DNA phosphate atom was measured and the shortest distance was plotted. Residues close to the core DNA or to the α3 and L1 linkers are shown in green, magenta, and blue respectively. DNA-distal residues are in black. The best-conserved residues localize close to nucleosomal DNA, while most DNA-distal residues are poorly conserved. Exceptions (conserved and DNA-distal; black squares) are Lys40, consistent with an alanine substitution of Lys40 having little effect on stability of the H1-nucleosome complex () (see panel D) and Ser41, which corresponds to an acidic residue in most H1 orthologs (). (D) Effect of alanine mutations on half-time of FRAP recovery (t50) plotted versus distance from DNA. FRAP data (mean ± S.D.) are those of (). Brackets indicate mutations with a strong, medium or weak effect on t50. See also .