scholarly journals ABERRANT INTRANUCLEOLAR MATURATION OF RIBOSOMAL PRECURSORS IN THE ABSENCE OF PROTEIN SYNTHESIS

1970 ◽  
Vol 45 (3) ◽  
pp. 554-564 ◽  
Author(s):  
Nessly C. Craig ◽  
Robert P. Perry
Keyword(s):  
Protein Synthesis ◽  
Ionic Strength ◽  
Ribosomal Rna ◽  
Buoyant Density ◽  
Protein Composition ◽  
28S Rrna ◽  
Maturation Process ◽  
Variable Response ◽  
Protein Complement

To help elucidate the role of protein in the maturation of ribosomal RNA in cultured L cells, we have studied the effects of cycloheximide upon the maturation process and upon the intranucleolar ribonucleoprotein particles containing the "preribosomal RNA's." Five parameters of these particles were analyzed: (a) extractability, (b) sedimentation characteristics in sucrose gradients, (c) RNA composition, (d) buoyant density in CsCl gradients, and (e) effects of increased ionic strength on the buoyant density. When protein synthesis is inhibited, the rate of conversion of the precursor 45S ribosomal RNA is rapidly diminished, falling to less than 30% of the control rate within 1 hr. Nevertheless, in terms of the first three parameters there is no difference between control and cycloheximide nucleolar particles. However, the cycloheximide particles have a lower and more heterogeneous buoyant density and a more variable response to increased ionic strength. The results imply that the protein composition of the cycloheximide particles is different from that of particles from control cells, and that the entire protein complement is not necessary for the first cleavages in the maturation process, although it is necessary for the normal rate of processing and for the eventual appearance of both 18S and 28S rRNA in mature ribosomes.

scholarly journals The role of ribosomal ribonucleic acid in the structure and function of mammalian brain ribosomes

1974 ◽  
Vol 143 (2) ◽  
pp. 419-426 ◽  
Author(s):  
Barbara Kay Grove ◽  
Terry C. Johnson
Keyword(s):  
Protein Synthesis ◽  
Protein Interactions ◽  
Chemical Properties ◽  
Chain Elongation ◽  
Synthetic Activity ◽  
Mammalian Brain ◽  
28S Rrna ◽  
Diethylaminoethyl Cellulose ◽  
Brain Ribosomes

In order to resolve the functional role of intact rRNA in polypeptide chain elongation mouse brain ribosomes were treated with dilute pancreatic or T1 RNAase (ribonuclease). After RNAase treatment, several physical–chemical properties as well as the functional activity of the ribosomes were measured. RNAase treatment resulted in the extensive hydrolysis of both 18S and 28S rRNA; however, the sedimentation properties of mono-ribosomes were unaltered and more than 90% of the relatively low-molecular-weight RNA fragments remained associated with ribosome particles. Analysis of the ability of RNAase-treated ribosomes to participate in cell-free protein synthesis showed that ribosomes with less than 2% intact rRNA retained more than 85% of their activity in polyphenylalanine incorporation. Proof that the incorporation of phenylalanine by ribosomes with hydrolysed rRNA actually represented active translocation was obtained by the effective inhibition of incorporation by diphtheria toxin. In addition, the oligopeptide products of protein synthesis could be identified by BD (benzoylated diethylaminoethyl)-cellulose column chromatography. Analysis of the size distribution of oligopeptides synthesized by normal and RNAase-treated ribosomes showed no significant differences which indicated that there was no change in the proportion of ribosomes engaged in protein synthesis. Thus strong RNA–protein and protein–protein interactions must serve to maintain the functional integrity of ribosomes even when the rRNA is extensively degraded. The ability of the enzyme-treated ribosomes to efficiently incorporate amino acids clearly demonstrated that ‘intact’ rRNA is not required for protein-synthetic activity.

scholarly journals The evolving role of ribosomes in the regulation of protein synthesis

2020 ◽  
Author(s):  
Karolina Gościńska ◽  
Ulrike Topf
Keyword(s):  
Protein Synthesis ◽  
Crucial Role ◽  
Protein Production ◽  
Protein Composition ◽  
Disease Development ◽  
Target Specificity ◽  
Cellular Homeostasis ◽  
Multiple Levels ◽  
Polypeptide Chains

Maintenance of the cellular homeostasis is firmly linked with protein synthesis. Therefore, it is tightly controlled at multiple levels. An advancement in quantitative techniques, mainly over the last decade, shed new light on the regulation of protein production, which pointed the ribosome as a new player. Ribosomes are macromolecular machines that synthesize polypeptide chains using mRNA as a template. The enormous complexity of ribosomes provides many possibilities of changes in their composition and consecutively in their target specificity. However, it is not clear how this specialization is enforced by the cell and which stimuli provoke that diversity. This review presents an overview of currently available knowledge about ribosome heterogeneity, focusing on changes in protein composition, and their role in the control of translation specificity. Importantly, besides the potential advantage of ribosome-mediated regulation of protein synthesis, its failure can play a crucial role in disease development.

scholarly journals Three tRNAs on the ribosome slow translation elongation

2017 ◽  
Vol 114 (52) ◽  
pp. 13691-13696 ◽  
Author(s):  
Junhong Choi ◽  
Joseph D. Puglisi
Keyword(s):  
Protein Synthesis ◽  
Ionic Strength ◽  
Binding Sites ◽  
Elongation Factor ◽  
Transfer Rna ◽  
Dissociation Kinetics ◽  
Translation Elongation ◽  
Trna Species ◽  
Trna Binding

During protein synthesis, the ribosome simultaneously binds up to three different transfer RNA (tRNA) molecules. Among the three tRNA binding sites, the regulatory role of the exit (E) site, where deacylated tRNA spontaneously dissociates from the translational complex, has remained elusive. Here we use two donor–quencher pairs to observe and correlate both the conformation of ribosomes and tRNAs as well as tRNA occupancy. Our results reveal a partially rotated state of the ribosome wherein all three tRNA sites are occupied during translation elongation. The appearance and lifetime of this state depend on the E-site tRNA dissociation kinetics, which may vary among tRNA species and depends on temperature and ionic strength. The 3-tRNA partially rotated state is not a proper substrate for elongation factor G (EF-G), thus inhibiting translocation until the E-site tRNA dissociates. Our result presents two parallel kinetic pathways during translation elongation, underscoring the ability of E-site codons to modulate the dynamics of protein synthesis.

The functional role of ribosomal RNA in protein synthesis

Cell ◽  
1989 ◽  
Vol 57 (4) ◽  
pp. 525-529 ◽  
Author(s):  
Albert E. Dahlberg
Keyword(s):  
Protein Synthesis ◽  
Ribosomal Rna ◽  
Functional Role

The role of ribosomal RNA in protein synthesis

FEBS Letters ◽  
1978 ◽  
Vol 94 (1) ◽  
pp. 139-144 ◽  
Author(s):  
D.H. Wreschner
Keyword(s):  
Protein Synthesis ◽  
Ribosomal Rna
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