An unusual precursor of 50S ribosomes in a mutant of Escherichia coli

Inhibition of bacterial ribosome assembly: a suitable drug target?

The assembly of bacterial ribosomes is viewed with increasing interest as a potential target for new antibiotics. The in vivo synthesis and assembly of ribosomes are briefly reviewed here, highlighting the many ways in which assembly can be perturbed. The process is compared with the model in vitro process from which much of our knowledge is derived. The coordinate synthesis of the ribosomal components is essential for their ordered and efficient assembly; antibiotics interfere with this coordination and therefore affect assembly. It has also been claimed that the binding of antibiotics to nascent ribosomes prevents their assembly. These two contrasting models of antibiotic action are compared and evaluated. Finally, the suitability and tractability of assembly as a drug target are assessed.

Partial deproteinization of ribosomal subunits by treatment with high concentrations of sodium chloride: physical and chemical characterization of protein depleted particles

Sedimentation of E. coli ribosomal subunits through sucrose gradients containing high concentrations of NaCl (0.1 - 1.0 M) brings about removal of a specific fraction of their proteins. The alterations in the structural properties of the subunits caused by dissociation of these proteins are studied. They appear to be, at least partly the result of removal of constraints on RNA conformation imposed by the released proteins.

Intermediates in the assembly of ribosomes by a mutant of Escherichia coli

Escherichia coli strain 15--28 is a mutant that accumulates ribonucleoprotein ('47 S') particles during exponential growth. These particles contain mature 23 S rRNA, but lack three of the proteins of the larger ribosomal subunit, to which they are a precursor. In organisms growing at 20 degrees C, assembly of 47 S particles involves three intermediates that contain precursor 23 S rRNA, one of which has the same sedimentation properties as 47 S particles. Assembly of 50 S ribosomal subunits in the parent strain is 'normal'. There are three intermediates; each contains precursor 23 S rRNA, and one cannot be distinguished from completed subunits by sedimentation. Synthesis of 30 S ribosomal subunits in parent and mutant strains is qualitatively similar, but quantitatively different. When growth is at 37 degrees C, assembly in the mutant alters. There are now two sequential precursors to 47 S particles. Both contain precursor 23 S rRNA; one has the same sedimentation coefficient as 47 S particles. In some respects, synthesis in the mutant proceeds as though 47 S particles, rather than 50 S ribosomal subunits, are the end-product of assembly.

Abnormal ribosome assembly in a mutant of Escherichia coli

The mutant strain, 15--28, of Escherichia coli accumulates ribonucleoprotein ('47S') particles that were previously shown [Markey, Sims & Wild (1976) Biochem. J. 158, 451--456] to be an unusual intermediate in the assembly of 50S ribosomal subunits...

Binding of chloramphenicol and a fragment of aminoacyl-transfer ribonucleic acid to ribosomes and a ribosome precursor from a mutant of Escherichia coli

During exponential growth, the mutatn strain Escherichia coli 15-28 accumulates 47S particles, which are unusual precursors to 50S ribosomal subunits. The 47S particles have little ability to bind chloramphenicol, but binding of a fragment of aminoacyl-tRNA is about half that by completed subunits. The 70S (and 50S) ribosomes of strain 15-28 and its parent (strain 15TP) do not differ in chloramphenicol binding. Although ribosomes from the mutant are less able than those from the parent to bind the fragment, this difference is not as marked as was found previously [Sims & Wild (1976) Biochem. J. 160, 721-726] for the binding of an analogue of peptidyl-tRNA and for peptidyltransferase activity. The altered activities may arise because strain 15-28 misassembles 50S subunits of altered conformation and because the few proteins that 47S patricles lack have vital functions in some of the partial reactions of protein synthesis.

Peptidyltransferase activity of ribosomes and a ribosome precursor from a mutant of Escherichia coli

Escherichia coli strain 15-28 is a mutant with a defect in ribosome synthesis that caused the accumulation of ribonucleoprotein ('47S') particles during exponential growth. These particles are precursors to 50S ribosomes that lack three ribosomal proteins. Peptidyltransferase activity and binding at the peptidyl site of the peptidyltransferase centre are greatly decreased in 47S particles. Both these activities are lower in the 50S and 70S ribosomes of strain 15-28 than in its parent. Unusual assembly of the larger ribosomal subunit in strain 15-28 may produce completed ribosomes with diminished biological activity.

The composition of an unusual precursor of 50 S ribosomes in a mutant of Escherichia coli

Escherichia coli strain 15--28 is a mutant which during exponential growth contains large amounts of a '47S' ribonucleoprotein precursor to 50S ribosomes. The '47S particles' are more sensitive to ribonuclease than are 50S ribosomes. The 23 S RNA of 47S particles may be slightly undermethylated, but cannot be distinguished from the 23S RNA of 50S ribosomes by sedimentation or electrophoresis. Isolated particles have 10--15% less protein than do 50S ribosomes; proteins L16, L28 and L33 are absent. Comparison with precursor particles studied by other workers in wild-type strains of E. coli suggests that the assembly of 50S ribosomes in strain 15--28 is atypical.