Sedimentation Studies on the Interaction of Ribosomal Subunits from Escherichia coli (I)

Intermediate stage in association and dissociation of ribosomes

Abstract

It is expected from the results by Tashiro & Siekevitz (1965) and Tamaoki &Miyazawa (1967) that E. coli ribosomes may dissociate into ribosomal subunits through the intermediate stage. To confirm the above possibility, we have examined the dissociation and association of E. coli ribosomes by sucrose density gradient using 0.1 mM crude extract and purified 100S ribosomes.
60S component and the dimer of derived 30S ribosomal subunits (intermediate components) were frequently observed in association of ribosomal subunits and the former seemed to be swollen 70S ribosomes weakly bound. These intermediate components were also observed in dissociation of 100S ribosomes, but it was only a few cases and most of them were observed when purified 100S ribosomes were layered onto a sucrose density gradient made with 10 mM Tris buffer containing 1 mM or 0.5 mM Mg²⁺ without dialysis and immediately centrifuged. In this case, we can't deny the possibility that 70S ribosomes may contaminate in the 50S particle region as a swollen 70S ribosome, because 70S ribosomes swell according to incomplete dissociation under the experimental conditions, and thereby the friction coefficient increases, which results in the decrease of the sedimentation coefficient of the swollen 70S ribosomes. The process of association and dissociation of E. coli ribosomes has been discussed and posturated.