Effects of temperature on the parameters of the DNA double helix in solution
Shchelkina, A.K.; Minchenkova, L.E.; Ivanov, V.I.
Molekuliarnaia Biologiia 11(2): 466-472
1977
ISSN/ISBN: 0026-8984 PMID: 379601 Document Number: 114502
The influence of temperature in the range -40.degree.-40.degree. C on DNA [from Escherichia coli] conformation was studied in water, water-methanol ad water-ethanol solutions of LiCl, NaCl, KCl and CsCl by circular dichroism (CD). In all cases the decrease in temperature results in winding of the helix as revealed by a drop in the CD magnitude at 276 nm. The temperature coefficients of this winding (d.DELTA.epsilon.276/dt) are different for different ions; with the exception of Li+, these make the series: Na+ > K+ .gtoreq. Cs+, which holds in all media. The obtained data are explained by Samoilov's concept postulating the hydration increase of the alkaline ions with temperature. The enlargement of the hydration shell of the ions with temperature decreases their ability to neutrlize phosphates and increases repulsion between the complementary chains forcing widening of the narrow (glycosidic) groove. Due to structural peculiarities of the double helix, this leads to a decrease in winding angle between the successive base pairs. Temperature coefficients of unwinding for different ions correlate with those of the electrolytic mobility of the same ions; this confirms the above explanation. An anomalous behavior of Li+ is discussed on the basis of the possible existence of the double layer hydration shell for this ion. The unwinding effects of temperature on the DNA double helix observed by the CD method are compared with those reported by for superhelical DNA.