Quantitative Aspects of Deoxyribonucleic Acid Renaturation: Base Composition, State of Chromosome Replication, and Polynucleotide Homologies

Abstract

The base composition of a deoxyribonucleic acid (DNA) sample affects its intrinsic rate of renaturation. In agreement with the information of Wetmur and Davidson, it was established that high guanosine plus cytosine (GC) DNA renatures faster than expected from analytical measurement of its molecular weight. A calculated correction factor of 1.8% of the observed C₀t_.5 is required for every mole per cent GC difference from 51% GC. The correction factor is now established in the range of 32 to 65% GC. Renaturation of DNA mixtures prepared from pairs of organisms has been studied. When no similarity existed between the two organisms, the observed C₀t_.5 of the mixture was the sum of the independently determined C₀t_.5 values. Lack of additivity was correlated with similarities in polynucleotide sequence of the reassociating DNA molecules. A quantitative relationship was formulated to relate C₀t_.5 values of renatured DNA mixtures to per cent binding (“homology”). Finally, it was demonstrated that DNA prepared from log-phase cells renatures faster than stationary-phase DNA and also departs from theoretical second-order kinetics.