Chromatin fine structure at the chicken lysozyme locus is reorganized prior to the onset of gene expression and the formation of stable transcription factor complexes. (A) UV photofootprinting experiment examining alterations in UV-dimer formation frequency with the clys promoter. The gels shown are representative of 2 independent experiments and 2 separate gels, respectively. G indicates DMS-treated naked genomic DNA; N, UV-treated naked genomic DNA; and EF, freshly prepared embryonic fibroblasts from transgenic mice. (B) UV photofootprinting of the -6.1 kb enhancer. The gels shown are representative of 2 independent experiments and 2 separate amplifications, respectively. (C) Quantification of bands from the gel depicted in panel B. The band intensity at each nucleotide position was divided by the band intensity of naked DNA and the ratio plotted as described previously.11 The nature and the position of transcription factor binding sites are indicated. The asterisk marks the position of extensive alterations in UV-dimer formation in differentiating cells as compared to naked DNA and EFs.
