Dissociation and reassembly of polyribosomes in relation to protein synthesis in the soybean root

Abstract

Polyribosomes of the soybean root rapidly dissociate under energy-depleting conditions, namely anaerobiosis and dinitrophenol treatment. The loss of polyribosomes cannot be attributed to a depletion of messenger RNA, because polyribosomes re-form to about 75% of the original level following restoration of aerobic conditions in the presence of dactinomycin. The dactinomycin treatment resulted in greater than 90% inhibition of RNA synthesis during the aerobic recovery period. Nascent polypeptide is lost from the ribosomes coincident with or during the conversion of polyribosomes to monoribosomes during anaerobiosis. Cycloheximide blocks both the conversion of polyribosomes to monoribosomes and the loss of nascent polypeptide from ribosomes. The results suggest that polyribosome dissociation occurs as a result of completion of read-out and release of polypeptide and monoribosome, coupled with a failure of attachment of ribosomes to messenger RNA and subsequent initiation of new peptide chains.