The ratio of free to thylakoid-bound chloroplast ribosomes in Chlamydomonas reinhardtii undergoes periodic changes during the synchronous light-dark cycle. In the light, when there is an increase in the chlorophyll content and synthesis of thylakoid membrane proteins, about 20-30% of the chloroplast ribosomes are bound to the thylakoid membranes. On the other hand, only a few or no bound riboso...

Methidiumpropyl-EDTA.Fe(II) [MPE.Fe(II)] and EDTA.Fe(II) were used to investigate the structure of Drosophila melanogaster ribosomes. Cleavage reactions were performed on intact ribosomes in cell lysates in vitro and analyzed by primer extension with reverse transcriptase using oligodeoxynucleotide primers. Regions of 18S and 28S ribosomal RNAs (rRNAs) which are accessible to MPE.Fe(II) and EDT...

30 and 50S ribosomal subunits, released from polysomes upon polypeptide chain termination, possess a high affinity for each other and readily form single ribosomes. Highly purified initiation factor F3(B), acting stoichiometrically, prevents the formation of single ribosomes without promoting their dissociation. These findings are interpreted in terms of a ribosome cycle in which a limiting amo...

Evidence is presented that indicates that greater than 95 % of the protein synthesized by intact rabbit reticulocytes is globin and that only globin nascent chains are found on the membrane-bound ribosomes from reticulocytes. This result conflicts with reports in the literature that approximately 14% of the protein synthesized by reticulocytes is non-globin and that 86% of the protein synthesiz...

The aminoglycosides, a group of structurally related antibiotics, bind to rRNA in the small subunit of the prokaryotic ribosome. Most aminoglycosides are inactive or weakly active against eukaryotic ribosomes. A major difference in the binding site for these antibiotics between prokaryotic and eukaryotic ribosomes is the identity of the nucleotide at position 1408 (Escherichia coli numbering), ...

The effect of various sulfhydryl reagents on the ribosomes of Bacillus subtilis was studied. The 70S ribosomes were completely dissociated into 30S and 50S subunits by appropriate concentrations of p-chloromercuribenzoic acid (PCMB) and 5,5'-dithio-bis-(2-nitro-benzoic acid). The N-ethylmaleimide and iodoacetamide failed to dissociate the ribosomes even at relatively high concentrations. The ra...

Rough microsomes were incubated in an in vitro amino acid-incorporating system for labeling the nascent polypeptide chains on the membrane-bound ribosomes . Sucrose density gradient analysis showed that ribosomes did not detach from the membranes during incorporation in vitro. Trypsin and chymotrypsin treatment of microsomes at 0 ° led to the detachment of ribosomes from the membranes ; further...

Rats intravenously injected with pilocarpine at a concentration of 4 mg per 100 g body weight were killed after various time intervals and the relative numbers of ribosomes per cell active in protein synthesis were determined. It was found that until 1 h after pilocarpine injection there is a significant decrease in the number of ribosomes engaged in protein synthesis, whereas 2--3 h after pilo...

Ribosomes are macromolecular machines that synthesize all cellular proteins. Ribosome biogenesis requires huge expenditure of cellular energy, and its dysregulation can result in a number of diseases including cancer. In vitro reconstitution experiments of bacterial ribosomal subunits have revealed principles underlying the assembly of ribosomes. These principles are also thought to guide the m...

The ribosome is universally responsible for synthesizing proteins by translating the genetic code transcribed in mRNA into an amino acid sequence. Ribosomes use cellular accessory proteins, soluble transfer RNAs, and metabolic energy to accomplish the initiation, elongation, and termination of peptide synthesis. In translocating processively along the mRNA template during the elongation cycle, ...