Pyrimidine dimer formation as a probe of nucleosome cove and linker structure in situ

The photoinduced dimerization of adjacent pyrimidines in DNA is influenced in predictable ways by DNA conformation. A method is described for determin ing patterns of pyrimidine dimer formation under conditions in which the ch romatin is minimally perturbed. The relation of such patterns to the confor mation of nucleosomal core DNA and linker DNA, as well as the interaction o f histone H1 with nucleosomal DNA, is presented. Such data indicate that sh arp bends in the path of DNA seen in crystals of isolated nucleosome core p articles are also present in intact chromatin. They also indicate that most of the linker has very little curvature except for a small bend at its jun ction with the nucleosome core. The linker path inferred from such experime nts supports models in which the chromatin fiber consists of a zigzag chain :of nucleosomes. (C) 1999 Academic Press.