Determination of the molecular complexity of double-stranded phage genome DNA from initial renaturation rates. The effect of DNA base composition.

Abstract

The molecular complexity of double-stranded phage genome DNA was determined by an adaptation of the initial renaturation rate method (Gillis et al., 1970) . The exact conditions, the reproducibility, the reliability and the effects of salt concentration, optimal temperature, renaturation time, DNA concentration and base composition were determined. The method is sensitive: a sample size of 20 determinations yields 4% confidence limits on the sample mean. The molecular complexity and length of genome DNA from several phages were determined. Our results agree perfectly with the most reliable values proposed by Freifelder (1970) . Our method appears to offer advantages by its rapidity, reproducibility and reliability. A statistical treatment shows that the available literature data on the molecular weight of bacterial and phage chromosome DNA, and on the length of phage chromosome DNA, of the same organisms are so widely scattered that an eventual effect of the DNA base composition on the renaturation rate is smaller than the experimental scatter. When the most reliable literature data on phage T5, T7 and λ+ genome sizes (Freifelder, 1970) are used in conjunction with our k′ measurements, the effect of the % (G+C) on the renaturation rate is negligible. We propose to disregard this effect until more precise reference data become available.