The relative homogeneity of microbial DNA

Abstract

Density-gradient centrifugation has revealed that the population of DNA molecules from E. coli is relatively homogeneous with respect to buoyant density in a solution of cesium chloride.(1) Because of the notably small apparent atomic volume of nitrogen in aqueous solutions of organic compounds(2) and because the guanine-cytosine base pair is more rich in nitrogen than is the adenine-thymine pair, it was considered that the density homogeneity among E. coli DNA molecules might reflect a high degree of homogeneity with respect to base composition. To investigate this possibility, an examination has been made of the relationship between buoyant density in cesium chloride solution and base composition of DNA from various sources.