Nucleic Acids Research, 1984, Vol. 12, No. 15 6325-6335
© 1984
CHEMISTRY |
A polycationic amine that induces unique conformational changes in poly(dA-dT) in low salt)
Department of Chemistry, University of Cincinnati Cincinnati, OH 45221, USA
Received March 15, 1984. Revised July 9, 1984. Accepted July 9, 1984.
Circular dichroism was used to examine alterations in the secondary structure of poly(dA-dT)·poly(dA-dT) upon binding polymer X, a polycationic CD probe for aspects of DNA structure. Stable complex formation is evidenced by increasing Tm and the appearance of large extrinsic bands in the > 300 nm, region which increase proportionally with r (ratio of polymer charge to DNA phosphate), in the range 0.0 to 0.32. At relatively low values of r (.32), CD spectra of the poly(dA-dT)·poly(dA-dT)-polymer X complex show a gradual non-cooperative inversion in the long wavelength portion (275 nm) of the intrinsic band in low salt solutions suggesting structural and conformational flexibility in poly(dA-dT)·poly(dA-dT) and further implicating polymer X as a potential probe for variations in DNA secondary structure. The dinucleotide repeat configuration of poly(dA dT)·poly(dA-dT) is presumed to play a role in the observed intrinsic CD changes. NMR data support an "alternating B" conformation for the complex.