We have discovered that the covalent attachment of amines to DNA based via a crosslinking reaction with CH2O produces a derivative which has the same conformational characteristics as DNA in concentrated electrolyte solution and complexed to core histones in core particles of chromatin. X-ray diffraction, Raman spectroscopy and winding angle studies reveal that the conformation produced by the amine attachment is a B conformational variant which may be moving to a C secondary structure. When the amine is attached to Poly (dGdC), it assumes the conformation appropriate for core histone complexion and does not convert to the Z form when subjected to the appropriate ionic environment. Using a combination of spectroscopic and enzymatic approaches, we propose to exploit these findings and the amine/CH2O reaction to (1) elucidate the origin of the conformational change in terms of the effect of specific positioning of positive charges in the grooves of the helix of the DNA molecule, (2) attempt to push the DNA in solution further along the conformational continuum to the C endpoint by suitable manipulation of amine substitution and environmental parameters, (3) delineate the role of substituents and charge on the B greater then Z conversion, and (4) test certain aspects of current polyelectrolyte theory. In addition to this program, we also intend to monitor the conformational effects of methylation on DNA of high m5C content, both free in solution, covalently complexed with amines and complexed with histone proteins. The results of these studies will hopefully shed some light on the role that transconformational changes in DNA plays in gene expression.
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