ABSTRACT
When putrescine is added to polyamine starved cultures of an E. coli strain difficient in the biosynthesis of putrescine, the protein synthesis is enhanced almost immediately and the ribosomal pattern changes concomitantly, increasing the ratio 70S monomer/ribosomal subparticles. Studies with cell-free systems derived from polyamine starved or unstarved bacteria show that the translation of synthetic and natural mRNAs is several fold higher in system prepared from cells grown in the presence of polyamines. This effect depends on the ribosomal particles and more specifically on the 30S subunit. The results on association of ribosomal subunits strongly suggest that polyamines are involved in this reaction occurring in vivo.
Subject(s)
Bacterial Proteins/biosynthesis , Escherichia coli/metabolism , Putrescine/metabolism , Ribosomal Proteins/biosynthesis , Animals , Polyamines/metabolism , RNA/biosynthesisABSTRACT
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.
