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PROTEIN SYNTHESIS BY CEREBRAL POLYSOMES PRETREATED WITH PUROMYCIN
Author(s) -
Murthy M. R. V.,
Roux Huguette
Publication year - 1974
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1974.tb11583.x
Subject(s) - puromycin , polysome , ribosome , protein biosynthesis , biochemistry , messenger rna , sucrose , microsome , centrifugation , biology , rna , chemistry , biophysics , enzyme , gene
— Polysomes prepared from rat cerebral microsomes, following preincubation with a high concentration of puromycin (2.5 mM) in the presence of rat liver soluble enzymes, were very similar to normal polysomes in yield, A 260 nm :A 280 nm ratio and in absorbance profile on sucrose density gradients. However, the capacity for amino acid incorporation was inhibited by more than 50 per cent by puromycin treatment. The extent of inhibition far exceeded what could be expected from the amount of residual puromycin bound to polysomes, suggesting that some essential step in polypeptide synthesis was damaged. An examination of the labelled polypeptides, using sucrose density gradient centrifugation, showed that most of the new chains synthesized by puromycin‐polysomes were released into solution. However, small amounts of polypeptides of high specific radioactivity were distributed among the polysomal aggregates. In contrast to normal polysomes, the specific radioactivity of puromycin polysomes was the highest in aggregates of six or more ribosomes and declined sharply at the levels of trimers and dimers. It is suggested that cerebral polysomes pretreated with puromycin become defective in the termination mechanism with the consequence that even though they are capable of moving at least short distances on the messenger RNA and of releasing the polypeptide chains formed, a concomittant release of monomeric ribosomes is obstructed. This may result in the‘clogging’of the terminus of the mRNA, thus blocking further polypeptide synthesis.