Composition of Various Ribonucleic Acid Fractions from Micro-organisms of Different Deoxyribonucleic Acid Composition
THE ratio of guanine plus cytosine to adenine plus thymine (GC/AT) in the deoxyribonucleic acid (DNA) of a given species of a micro-organism is constant, but the GC/AT ratio of different kinds of microorganisms can vary by a factor of as much as five times1. The ratio of GC content to AU (uracil) content of cell ribonucleic acid (RNA) varies only slightly from one organism to another; but this ratio tends to be slightly higher in organisms the DNA ratio of which is high2. These facts raise a question as to whether all the RNA of a cell has the same composition or whether perhaps a small RNA sub-fraction has the same base ratios as its corresponding DNA (uracil being equivalent to thymine). Recent experiments have demonstrated an RNA sub-fraction in yeast which does have a composition almost identical to the corresponding DNA (ref. 3). The present work is concerned with analysing the nucleotide ratios in sub-fractions of the RNA from organisms with varying GC/AT ratios in the DNA.