The Structural Organization of Ribonucleic Acid Associated with Soybean Microsomes

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Abstract
The microsomal fraction of soybean (Glycine max) hypocotyls was characterized using analytical and electron microscope techniques. Two microsomal sub-fractions (smooth and rough vesicles) were separated by untracentrifugation. Analysis showed that the ribonucleic acid (RNA) of the microsomal fraction cannot be completely accounted for by the ribosomes, and that some of the RNA is associated with the membranes in a non-ribosomal form. A similar conclusion was reached by using ethylenediaminetetra-acetic acid (EDTA) to disperse the ribosomal material. Although no visible robosomes remained after the treatment with EDTA, the microsomal fraction retained a quarter of its RNA. Ribonuclease removed all the mocrosomal RNA without visibly altering the membrane structure examined in cross section. When hypocotyl tissue sections were incubated with 14C amino-acids, the microsomes incorporated the radioactive label more rapidly than any other subcellular fraction. This was especially true in the rapidly growing zone of the hypocotyl. Smooth microsomes were 75 per cent as active as rough microsomes. These observations are discussed with reference to the structural organization of the microsomal RNA and its role in protein synthesis.

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