DETERMINATION OF DNA BASE COMPOSITIONS FROM MELTING PROFILES IN DILUTE BUFFERS

Equations were determined for the dependency of the melting temperature (Tm) of DNA upon the logarithm of the sodium ion concentration, for four DNA samples of widely different base compositions (θGC). The slopes of these Tm versus log M equations wore found to decrease with increasing θG Cof the samples. An empirical equation relating Tm, log M (Na+) and θG C was derived, which also accounts for differences in Tm versus log M slopes. Data from the literature for some synthetic polynucleotides and for the crab(Cancer pagarus) satellite poly AT are discussed in relation to the above finding. The changes in Tm versus log M slopes with θG C are interpreted in terms of changes in the thermodynamic parameters ΔS and ΔH with base composition. Copyright © 1969 John Wiley & Sons, Inc.