Ultraviolet laser footprinting of histone H1°-four-way junction DNA complexes

We have used a new light footprinting technique to study the interaction of histone H1 degrees and a deletion mutant delta CH1 degrees (lacking H1 degrees 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 degrees and delta CH1 degrees 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 degrees for the central domain of four-way junction DNA. In addition, histone H1 degrees decreases the photorectivity of selected guanines located some distance from the crossover, indicating specific involvement of the H1 degrees COOH-tenninal tail with this region. Immunofractionation of delta CH1 degrees-four-way DNA junction complexes with monoclonal anti-H1 degrees antibody combined with the UV laser footprinting method demonstrated the existence of two types of delta CH1 degrees-four-way DNA junction complexes.