Ribosome biogenesis: nonrandom addition of structural proteins to 50S subunits.

Assemblage of structural proteins into 50S subunits was examined in Escherichia coli recovering fromt chloramphenicol treatment. Cells previously labeled with H3-leucine for three generations were incuibated for 30 minutes with chloramnlphenicol. Proteins synthesized during the initial 5 minuites of recovery from chlorarmphenicol treatmnent were labeled with C(14)-leucine. Marked variation in the ratios of C(14)- to H(3)-leucine in ribosomal protein occurred in cells that had been treated with chloramphenicol; luntreated cells displayed little variation. Thle resuilts sliggest that ribosomal proteins are assenmbled into 50S subunits in a nonrandom manner.