Structure and Function of Bacterial Ribosomes, XI. Dependence of 50S Ribosomal Assembly on Simultaneous Assembly of 30S Subunits

Some spectinomycin-resistant mutants of Escherichia coli are cold-sensitive. They are unable to assemble both 30S and 50S ribosomal subunits at low temperatures. They accumulate two kinds of incomplete particles, related to 30S and 50S subunits respectively. A single mutation, causing an alteration in a 30S ribosomal component, is responsible for these phenotypes. These results show that assembly of 50S subunits in vivo is dependent on simultaneous assembly of 30S subunits. On the other hand, the assembly of 30S subunits appears to be independent of 50S assembly.