Ultraviolet Laser Footprinting of Histone H1°−Four-Way Junction DNA Complexes

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Abstract
We have used a new light footprinting technique to study the interaction of histone H1° and a deletion mutant δCH1° (lacking H1° COOH-terminal domain) with a synthetic four-way junction DNA. This technique is based on a single 5-ns UV laser pulse and has the ability to map protein−DNA interactions within unperturbed complexes at time scales far faster than molecular rearrangements. We found both H1° and δCH1° to affect the photoreactivity of specific guanine residues located on the central part of four-way junction DNA. These observations demonstrate specific recognition of H1° for the central domain of four-way junction DNA. In addition, histone H1° decreases the photorectivity of selected guanines located some distance from the crossover, indicating specific involvement of the H1° COOH-terminal tail with this region. Immunofractionation of δCH1°−four-way DNA junction complexes with monoclonal anti-H1° antibody combined with the UV laser footprinting method demonstrated the existence of two types of δCH1°−four-way DNA junction complexes.