Divalent Metal- and High Mobility Group N Protein-Dependent Nucleosome Stability and Conformation
Figure 1
HMGN binding to the nucleosome core is ion dependent and capable of eliciting a transition. Gel labels indicate HMGN identity (N1t, HMGN1t; N1, HMGN1; N2, HMGN2; n, NCP alone; a, nucleosome array alone), and numbers designate HMGN : nucleosome molar stoichiometry. (a) EMSAs of HMGN binding to two distinct NCP constructs, NCP-601 (left) and NCP147 (right), under three different buffer conditions: low ionic strength (top), near physiological ionic strength (middle), and near physiological ionic strength with 1 mM Mg2+ (bottom). Under noncooperative binding conditions (top), 1 : 1 as well as 2 : 1 HMGN : nucleosome species are observed at low stoichiometry [12]. At higher ionic strength (middle), 2 : 1 species (S1) are the only specific complexes that occur. In the presence of divalent metal, a distinct, slow-migrating species (S2) is also observed for HMGN1t and HMGN2 binding. (b) EMSA showing migration rate for S1 and S2 of NCP-601 (HMGN : nucleosome = 4 : 1) relative to NCP and a 4-nucleosome array. (c) SDS-polyacrylamide gel analysis of HMGN purification products (see Methods). Samples from HMGN1 (left) and HMGN2 (right) overexpression are shown for crude extract (cr) and after gel filtration (gf) and ion-exchange chromatography (N1, N1t, and N2). (d) Xenopus HMGN primary structures. Functional domains are the NBD (blue) and RD (red). Nuclear localization elements are shown in green.
