The article by U. E. Loening describes the fractionation of high-molecular-weight ribonucleic acid (RNA) using polyacrylamide-gel electrophoresis. The method involves preparing gels with recrystallized acrylamide and bisacrylamide, and performing electrophoresis in a tris-sodium acetate-EDTA buffer for 0.5 to 3 hours. The mobility of RNA is inversely related to its sedimentation coefficient and varies with gel concentration. In 2.2-2.6% gels, similar fractionation to density-gradient centrifugation is achieved, resolving the two ribosomal RNA components, transfer RNA, and minor components. In 5% and 7.5% gels, 4S and 5S RNA are separated, and ribosomal RNA is excluded. The resolution is greater than that of centrifugation, allowing simultaneous and rapid analysis of multiple samples. The method has been successfully used to separate ribosomal RNA components and minor components, with excellent separations obtained. The article details the preparation of gels, electrophoresis procedures, and scanning techniques for ultraviolet absorption and radioactivity. Examples of RNA fractionation from rabbit reticulocyte polysomes, E. coli, pea seedling root tips, and various organisms are provided, demonstrating the method's potential for analytical and preparative applications.The article by U. E. Loening describes the fractionation of high-molecular-weight ribonucleic acid (RNA) using polyacrylamide-gel electrophoresis. The method involves preparing gels with recrystallized acrylamide and bisacrylamide, and performing electrophoresis in a tris-sodium acetate-EDTA buffer for 0.5 to 3 hours. The mobility of RNA is inversely related to its sedimentation coefficient and varies with gel concentration. In 2.2-2.6% gels, similar fractionation to density-gradient centrifugation is achieved, resolving the two ribosomal RNA components, transfer RNA, and minor components. In 5% and 7.5% gels, 4S and 5S RNA are separated, and ribosomal RNA is excluded. The resolution is greater than that of centrifugation, allowing simultaneous and rapid analysis of multiple samples. The method has been successfully used to separate ribosomal RNA components and minor components, with excellent separations obtained. The article details the preparation of gels, electrophoresis procedures, and scanning techniques for ultraviolet absorption and radioactivity. Examples of RNA fractionation from rabbit reticulocyte polysomes, E. coli, pea seedling root tips, and various organisms are provided, demonstrating the method's potential for analytical and preparative applications.