HISTONE H1 IS LOCATED IN THE INTERIOR OF THE CHROMATIN 30-NM FILAMENT

THE linker histone H1 binds to the nucleosome and is essential for the organization of nucleosomes into the 30-nm filament of chromatin(1). It has been implicated in the repression of transcription(2,5), and ph osphorylation of H1 may be involved in cell-cycle-dependent chromatin condensation and decondensation(6). A long-standing issue concerns the location of H1 in the chromatin filament(7). The original solenoidal model(8) proposes that H1 is inside the 30-nm filament, but other mode ls, also helical, suggest a variable(9) or more accessible(10) locatio n for H1. Investigations to determine the location of the linker histo ne based on its accessibility to antibodies(11-15) or immobilized prot eases(16) under various ionic conditions have yielded conflicting resu lts. Here we use neutron scattering in a direct structural determinati on to show that H1 is located in the interior of the filament.