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

Rpl33, a nonessential plastid-encoded ribosomal protein in tobacco, is required under cold stress conditions

Plastid genomes contain a conserved set of genes encoding components of the translational apparatus. While knockout of plastid translation is lethal in tobacco (Nicotiana tabacum), it is not known whether each individual component of the plastid ribosome is essential. Here, we used reverse genetics to test whether several plastid genome-encoded ribosomal proteins are essential. We found that, while ribosomal proteins Rps2, Rps4, and Rpl20 are essential for cell survival, knockout of the gene encoding ribosomal protein Rpl33 did not affect plant viability and growth under standard conditions. However, when plants were exposed to low temperature stress, recovery of Rpl33 knockout plants was severely compromised, indicating that Rpl33 is required for sustaining sufficient plastid translation capacity in the cold. These findings uncover an important role for plastid translation in plant tolerance to chilling stress.

The effects of mutations in the rpmB,G operon of Escherichia coli on ribosome assembly and ribosomal protein synthesis

The rpmB,G operon of Escherichia coli codes for proteins L28 and L33 of the larger (50S) ribosomal subunit. Strains with mutations in this operon can help define the roles of these proteins in ribosome synthesis and function. One such strain, BM108, makes neither protein and is unable to synthesize completed ribosomes; instead ribonucleoproteins accumulate, in the form of '30S material' and '47S particles'. However, when protein L28 is supplied from a plasmid, the growth rate, the kinetics of ribosome synthesis and the coordination of ribosomal protein synthesis are no different from that in wild-type organisms even though protein L33 is missing. This suggests that the latter protein can be redundant for ribosome synthesis and function. Another mutant strain, BM81, has a frameshift mutation that gives rise to an oversized protein L28. This mutant accumulates 30S material and 47S particles during slow exponential growth. The composition of the 47S particles from strains BM81, BM108 and a third mutant strain, TP28, suggests that their defining feature is the absence of L28; this is further evidence for an important role for this protein in ribosome assembly. Accumulation of ribonucleoproteins in strains BM81 and BM108 leads to some loss of the ordinarily precise coordination of synthesis of ribosomal proteins. We describe and discuss the characteristic features of this unbalanced synthesis.

Mutations in the rpmBG operon of Escherichia coli that affect ribosome assembly

The rpmBG operon of Escherichia coli codes for ribosomal proteins L28 and L33. Two strains with mutations in the operon are AM81, whose ribosomes lack protein L28, and AM90, whose ribosomes are without protein L33. Neither strain showed major defects in ribosome assembly. However, when the mutations were transferred to other strains of E. coli, ribosome synthesis was greatly perturbed and precursor ribonucleoproteins accumulated. In the new backgrounds, the mutation in rpmB was complemented by synthesis of protein L28 from a plasmid; the rpmG mutation was not complemented by protein L33 because synthesis of protein L28 from the upstream rpmB gene was also greatly reduced. The results suggest that protein L33, in contrast to protein L28, has at best a minor role in ribosome assembly and function.

Ribosomal protein synthesis by a mutant of Escherichia coli

The mutant strain of Escherichia coli, TP28, synthesises ribosomes by an abnormal pathway and accumulates large quantities of 47S ribonucleoprotein particles. The protein complement of mutant 70S ribosomes is normal but 47S particles contain only traces of proteins L28 and L33 and have a significantly reduced content of four other proteins. The mutation reduces the rates of synthesis of L28 and L33 by about half but other widespread alterations ensue. In particular, ribosomal protein synthesis in the mutant strain becomes less well balanced than in its parent: some proteins, particularly those from promoter-proximal genes, are oversynthesized and their excess then degraded.

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.