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 photoreactivity 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.
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