Association of ribosomal subunits. IV. Polyamines as active components of the association factor from Bacillus stearothermophilus

Polyamine concentration, activity of the ribosomal dissociation factor and proportion of ribosomes active in protein synthesis in the 4-dimethylaminoazobenzene-induced rat hepatoma

4-Dimethylaminoazobenzene (DAB) induced liver tumour tissue showed a reduced proportion of ribosomes active in protein synthesis compared with control liver. Tumour cell extracts caused an increased association of ribosome subunits into inactive 80 S monomers, compared with the dissociation into active subunits caused by normal liver extracts. These findings may be explained, at least in part, by the increased proportion of spermidine to putrescine found in tumour tissue which would predispose towards association of the subunits.

Mechanism of protein synthesis inhibition during stationary phase in Bacillus stearothermophilus

The appearance of a protein (association factor I) in ribosomes from Bacillus stearothermophilus at stationary phase of growth is described. Association factor I is present on 30S subunits and 30S-50S ribosomal couples, but not on 50S subunits. This protein is responsible for the low levels of polyphenylalanine synthesis shown by stationary phase ribosomes. Association factor I is able to bind to free 30S-50S ribonsomal couples but not to polysomes, and exerts its effect by inhibiting the initiation step of protein synthesis. Ribonsomes preincubated with association factor I have a decreased ability for polypeptide synthesis directed page mRNA or poly(U).

Reassociation of eukaryotic ribosomal subunits by a factor from rat ascites hepatoma cytosol

Post-ribosomal supernatant extracts from Yoshida AH 130 ascites hepatoma cells promote the in vitro association of ribosomal subunits at low Mg2+ concentration. Comparable extracts from rat liver show, on the contrary, dissociation factor activity on ribosome monomers.

Ribosomal distribution in a polyamine auxotroph of Escherichia coli

The distribution of ribosomal particles has been studied in a polyamine-deficient mutant of Escherichia coli by sucrose gradient centrifugation analysis. Lysates from starved cells contained less 70S monomers and 30S subunits but more 50S particles than those prepared from bacteria supplemented with putrescine. The addition of the polyamine to putrescine-depleted cells induced a rapid change of the ribosomal profile. A similar effect could be obtained in vitro by equilibrium dialysis against a polyamine-containing solution. The ribosomal pattern obtained from starved bacteria was specific for polyamine deficiency. We conclude that the changes in ribosomal profiles upon restoration of putrescine levels in previously starved cells denote a shift of the equilibrium between 30S-50S couples and ribosomal subunits.