PMID: 6108955Jan 10, 1981Paper

The number of copies of ribosome-bound proteins L7 and L12 required for protein synthesis activity.

The Journal of Biological Chemistry
C C LeeB Wittmann-Liebold

Abstract

Poly(U)-dependent poly(Phe) synthesis and elongation factor G (EF-G)-dependent GTPase activity were used to study the partial reconstitution of L7/L12-deficient ribosomes with proteins L7/L12 and fluorescent conjugates. Seventy-five per cent of these activities are restored when unmodified L7/L12 dimer is added to L7/L12-deficient cores at a ratio of 1:1. Various covalent fluorescent conjugates of L7/L12 bind to these cores about as well as unmodified protein. A fluorescein-5-isothiocyanate derivative of L12 shows almost no functional activity when bound. However, mixed reconstitutes of this conjugate and unmodified L12 have 75% functional activity when half the protein is unmodified. These results can be explained by a model in which there are two independent binding sites on the ribosome for two dimers of L7/L12. The binding of dimers to ribosomes is totally random and complete; the particle is 100% active so long as it has one active dimer bound to either one of the two sites. However, more complex models cannot be ruled out. An 5-(iodoacetamidoethyl)-aminonaphthalene-1-sulfonic acid (IAEDANS) derivative of L7 is labeled semispecifically at the COOH terminus. This conjugate shows partial functional activity. When assay resul...Continue Reading

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