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Polyribosomes from Peas

An Improved Method for Their Isolation in the Absence of Ribonuclease Inhibitors ¹

^a Department of Botany, University of Nebraska, Lincoln, Nebraska 68508

Profiles of polyribosomes were obtained from etiolated stem segments of Pisum sativum L. var. Alaska isolated in various buffers. Tissue homogenized in a medium containing 0.2 M tris-HCl, pH 8.5, 0.2 M sucrose, 30 mM MgCl₂, and 60 mM KCl yielded polyribosomes exhibiting far less degradation than tissue homogenized in conventional media containing tris-HCl at lower ionic strength and pH. A further decrease in degradation was found when polyribosomes were sedimented through a sucrose pad buffered at pH 8.5 prior to centrifugation. Increased separation was obtained using heavy (125-500 mg/ml), linear sucrose gradients. Using these techniques, messenger RNA species bearing up to 12 ribosomes (dodecamers) were resolved, with messenger RNA chains bearing 9 ribosomes (nonamers) being the most abundant (having the highest absorption peak). The data presented suggest that buffer of high ionic strength and high pH was more effective in preventing degradation of polyribosomes than was diethyl pyrocarbonate and, furthermore, that ratios involving large polyribosomes (hexamers and larger) were more accurate indices of degradation than were ratios involving total polyribosomes.