Dissociation of N2 Gas-induced Monomeric Ribosomes and Functioning of the Derived Subunits in Protein Synthesis in Pea

The dissociation of N(2) gas-induced monomeric ribosomes from the pea root was studied by varying the concentration of KCl (or NH(4)Cl) and MgCl(2) in the presence of dithiothreitol. These monoribosomes were shown to dissociate completely into subunits at 0.5m KCl or NH(4)Cl in the presence of 5 mm MgCl(2). The 40S subunits were more susceptible to structural change in KCl than were the 60S subunits. On the other hand, the 60S subunits appeared to be more labile to NH(4)Cl.The activity of the subunits relative to aminoacyl-tRNA binding and peptide bond formation was investigated using subunits derived from 0.5 m KCl (or NH(4)Cl) in the absence and presence of 5 mm MgCl(2). The 40S subunits were active in aminoacyl-tRNA binding only when dissociated in the presence of MgCl(2). The 40S and 60S subunits combined in the presence of poly U were active in incorporation of (14)C-phenylalanine from (14)C-phenylalanyl-tRNA only when dissociation was achieved in the presence of 5 mm MgCl(2). The KCl-dissociated subunits were much more active in protein synthesis than NH(4)Cl-dissociated subunits.