Analysis of the thermal transition curves of deoxyribonucleic acid from microorganisms

The thermal transition of sheared deoxyribonucleic acid (DNA) may reveal differing nucleotide frequencies within individual fragments, which is a crude reflection of nucleotide sequence in the intact molecule. DNA samples from seven species were characterized at three molecular weights, encompassing a size range from about one one-hundredth to one ten-thousandth of the original molecules. Thermal denaturation curves were treated as cumulative frequency distributions of individual molecular fragments differing in average base composition. Thermal transition curves of individual DNA samples show characteristic deviations from normality, which indicates that the proportions of nucleotides in some DNA fragments differ considerably from the average for the intact molecule. The statistical values describing denaturation curves are characteristic and constant for DNA from a given organism and are different and distinctive for different organisms.