Photoaffinity Labeling of Chromatin

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Abstract
The syntheses and properties of potential photoaffinity labels for the proteins in chromatin studies are described. One compound, N,N''-bis-(9-acridinyl)-4-aza-4-(4-azidobenzoyl)-1,7-diaminoheptane dihydrochloride, was studied more closely. This photolabel shows high affinity towards [calf thymus] DNA (Ka .apprxeq. 3 .times. 105 M-1) and photoreacts with histones at wavelengths in the range 260-450 nm. The photoreaction was monitored fluorimetrically, and labeling of histones H1, H2A/H2B and H3 was observed. When chromatin was photolabeled, labeling of H1 was exclusively quenched by NaCl at concentrations which are known to cause dissociation of this histone from the DNA. Evidently, only DNA-associated proteins are photolabeled by the reagent.