DNA, rRNA and RNA partition isotherms rapidly labeled in a saline solvent system

Abstract

AbstractPartition isotherms of DNA, rRNA, and rapidly labeled RNA in a salt solvent system are determined. In the salt solvent system PMB (potassium phosphate buffer 1.50 M pH 7.0:2‐methoxyethanol:2‐butoxyethanol; 3:1:variable volume), equilibrated at the temperature T, the partition isotherms of animal ribosomal RNA and DNA form a series of straight lines according to the basic relation log k = B − AT(BuO), where k is the partition coefficient, B and AT are parameters depending upon the base composition, the molecular weight, the helix content, and conformation of nucleic acids, and (BuO) refers to the 2‐butoxyethanol amount in volume percent. This relation is also valid for other nucleic acid compounds (bases, nucleosides, nucleotides, oligoribonucleotides, and transfer RNA). For RNA fractions distributed in different Kirby salt solvent systems, log k is proportional to the relative levels of adenine and guanine expressed as the A/(A+G) ratio.Partition isotherms of high molecular weight RNA from mouse plasmocytoma, labeled during a few hours, are not straight lines. This behavior indicates a heterogeneous RNA population. By plotting the specific activity of this mixture (rRNA and rapidly labeled RNA) determined in the top phase of our salt solvent system as a function of the 2‐but‐oxyethanol content, we obtained a sigmoidal curve, which characterizes the nature of the RNA population investigated. Formulas are given for the calculation of the specific activities of rRNA and rapidly labeled RNA and for the calculation of their relative ratio.