Characterization of ribosomes from the seed of Pinus lambertiana

Ribosomes isolated from seeds of the sugar pine, Pinus lambertiana, have been characterized: The ribosome has a sedimentation coefficient (s_20,w⁰) of 78·2 S and contains 41 % RNA and 58 % protein. On dialysis against buffer containing 0·5-1 mM MgCl₂, the ribosome was reversibly transformed into an intermediate form (60 S). Further removal of Mg²⁺ causes the intermediate ribosome to dissociate into subunits (30 S and 40 S). Treatment of the intermediate ribosome with p-chloromercuribenzoic acid caused the dissociation of the particle into subunits. Incubating the 80 S ribosome with the sulfhydryl reagent caused a rapid transformation of the particle into an intermediate type particle. These results suggest that sulfhydryl groups are involved not only in associating the subunits but also in maintaining the compact structure of the ribosomes. The ribosome contains three ribosomal RNA components of 28 S, 18 S and 5 S. The base compositions of the three ribosomal RNA components are different.