Binding sites of ribosomal proteins on two specific fragments derived from Escherichia coli 50 S ribosomes.

Abstract

Escherichia coli 50 S ribosomes were digested by pancreatic RNAase under conditions which lead to the cleavage of the 23 S into two specific fragments. After removal of about half of the proteins (split proteins) by treatment with lithium chloride, the subparticles (core fragments) were separated and their proteins (core proteins) analyzed. Only four core proteins were bound exclusively to one or the other of the core fragments; each of the other core proteins was found on both fragments in constant proportion. In reconstitution experiments, a class of split proteins was found which did not recombine with the individual core fragments but which bound to a mixture of both. Without demonstrating the homogeneity of the 50 S ribosomes population, these results suggest that the ribosomal proteins are not randomly distributed in the complete 50 S subunit although most of them bind to multiple sites.