The Size of Ribosomal Subunit RNA in Amoeba discoïdes

Abstract

SUCROSE density gradient studies of ribosomes of large, free-living amoebae have given estimates for amoeba rRNA of 305 and 195, slightly in excess of the ribosomal subunit RNAs from mammalian cells¹. A more precise estimate of the molecular weights of RNA molecules is given by polyacrylamide gel electrophoresis, and a direct measure may be obtained as there is a linear relationship between electrophoretic mobility and the logarithm of the assumed molecular weight². It has been shown, however, that conformational differences between RNA species cannot be ignored in aqueous gel systems, and the recently developed non-aqueous system using formamide as a solvent offers a method of estimating relative molecular weights after the elimination of conformational effects on electrophoretic mobility³. We have found that under both aqueous and non-aqueous conditions of polyacrylamide gel electrophoresis, the rRNA of the amoeba large subunit was consistently smaller than that of mammalian cells, while the rRNA of the amoeba small subunit was consistently larger.