Conformation of DNA in chromatin reconstituted from poly [d(A-T)] and the core histones.

Present results provide direct evidence of the nature of a conformational change in DNA when nucleosomes are formed from core histones and poly [d(A-T)]. First, we have found some features which have characteristic aspects of the A like conformation of DNA. Thus, an increased contribution due to a sugar conformation close to C3'-endo puckering is detected in the Raman spectra. In addition, the circular dichroism (C.D.) spectra of reconstituted chromatin with poly [d(A-T)] exhibits an increases intensity at about 262 nm. A second feature acquired by poly [d(A-T)] in nucleosome formation from core histones is related to the presence of a negative band at about 280 nm in the C.D.spectra. The nature of this change is correlated with a DNA conformation characterized by a decreased number of base pairs per turn (28,29). This indicates that these two features of reconstituted nucleosomes reflect the presence of two types of DNA conformations, which overall form is of the B type (22,36).