FIG. 1.

Dose-response curve for reconstituted nucleosomes. (A) Nucleosome particles are efficiently reconstituted by octamer transfer. Thirty nanograms of the ³²P-labeled 180-bp probe DNA containing five centered GAL4 binding sites was reconstituted into nucleosome cores by the octamer transfer method. The mobilities of the nucleosome core (Nuc) and the naked DNA are indicated. The concentrations of donor nucleosomes were 0.1 μg (lane 1), 0.5 μg (lane 2), 1 μg (lane 3), and 3 μg (lane 4). (B) UV laser-induced histone-DNA cross-linking proceeds via a biphotonic mechanism. Reconstituted nucleosomes were irradiated with a single 266-nm laser pulse at different intensities. The amount of cross-linked ³²P-labeled DNA was measured by the phenol extraction procedure and plotted against the laser intensity. The experimental points were computer fitted to reflect two-quantum processes (4, 5).