Calibration of the change in thermal stability of DNA duplexes and degree of base pair mismatch

Abstract

One method of determining the degree of base pair divergence between two sources of DNA (different strains, species, etc.) is to determine the decrease in thermal stability of hybrid duplex DNA due to mismatching of base pairs. Attempts to calibrate the change in median melting temperature (ΔT_m) to base pair mismatch have led to conflicting results. We have studied the ΔT_m between DNAs of known sequence over a range of from 0.55% to 7.2% base pair mismatch. The relationship of ΔT_m and percent base pair mismatch is remarkably linear over this range with a correlation coefficient >0.98. A ΔT_m of 1°C corresponds to 1.7% base pair mismatch. This conversion is higher than that usually assumed and, therefore, rates of DNA evolution estimated by DNA-DNA hybridization studies are likely faster than previously thought.