Sypherd, Paul S. (University of California, San Diego). Formation of ribosomes from precursor ribonucleoprotein particles. J. Bacteriol. 90:411-417. 1965.-Amino acid deprivation of a "relaxed" mutant leads to the accumulation of ribonucleoprotein particles. The possibility that these particles are equivalent to normal ribosome precursors was investigated. This was accomplished by determining the fate of such particles after the termination of starvation, and subsequent growth. It was found that both the nucleic acid and the protein moieties of the "relaxed" particles were converted to mature ribosomes during the recovery phase. From kinetic measurements with "relaxed" particles and normal ribosome precursors, it was shown that they were metabolically indistinguishable. It was concluded that the ribonucleoprotein "relaxed" particles accumulated by the relaxed mutant are immature ribosomes, and equivalent to ribosome precursors which occur under normal growth conditions.