TEMPERATURE-DEPENDENT ULTRAVIOLET RESONANCE RAMAN-SPECTROSCOPY OF THEPREMELTING STATE OF DA-CENTER-DOT-DT DNA

Poly(dA) . poly(dT) and DNA duplex with four or more adenine bases in a row exhibits a broad, solid-state structural premelting transition a t about 35 degrees C. The low-temperature structure is correlated with the phenomena of ''bent DNA.'' We have conducted temperature-dependen t ultraviolet resonance Raman measurements of the structural transitio n using poly(dA) . poly(dT) at physiological salt conditions, and are able to identify, between the high and low temperature limits, changes in the vibrational frequencies associated with the C4 carbonyl[ stret ching mode in the thymine ring and the N6 scissors mode of the amine i n the adenine ring of poly(dA) . poly(dT). This work supports the mode l that the oligo-dA tracts' solid-state structural premelting transiti on is due to a set of cross-strand bifurcated hydrogen bonds between c onsecutive dA . dT pairs.