J. Biochem, 1976, Vol. 80, No. 2 277-282
© 1976 Japanese Biochemical Society
research-article |
Conformational Changes and Reassociation Properties of Small Subunits of Escherichia coli Ribosomes
*Department of Biophysical Chemistry, Dokkyo University School of Medicine Mibu, Tochigi 321-02
**Department of Chemistry, Faculty of Science, Science University of Tokyo Shinjuku-ku, Tokyo 162
Studies on the reassociation of ribosomal subunits from Escherichia coli were carried out using an ultracentrifuge equipped with a UV absorption scanner, and the conformational changes of ribosomal subunits were followed by circular dichroism measurements. Reassociation between the fractionated 30S and 50S subunits was promoted by the addition of uncharged tRNA at 4°. Furthermore, a sharp increase in the amount of reassociated products was observed on treatment of the sample solution at temperatures above 25°. Treatment at higher temperature only affected 30S ribosomal subunits. From CD measurements of Mg2+ concentration dependence for both ribosomal subunits, a significant decrease in molar ellipticity [
] at the 264 nm positive peak and a slight change of [] at the 222 nm band were observed for both subunits in dissociation buffer. Samples of 30S subunits pretreated at 37° for 40 min showed a small CD change at the 222 nm band. The same samples showed a slight increase in S value and enhanced ability to form 70S particles with 50S subunits. On the other hand, we detected no significant changes in CD spectra, S value or the ability to form 70 S particles with 50 S ribosomal samples subjected to same heat treatments.