In mammalian cells, as well as Escherichia coli, ribosomes translating membrane proteins interact cotranslationally with translocons in the membrane, and this interaction is essential for proper insertion of nascent polypeptides into the membrane. Both the signal recognition particle (SRP) and its receptor (SR) are required for functional association of ribosomes translating integral membrane p...

80 S ribosomes and elongation factors 1 and 2 (EF-1 and EF-2), isolated from freeze-dried porcine brain of the hypothalamic region, were used to study the interrelation between the ribosomal binding of the two factors and of phenylalanyltRNA and N-acetyl-phenylalanyl-tRNA. Complexing of ribosomes with EF-2 + /3, y-methylene-guanosine S’-triphosphate or EF-2 + GTP + fusidic acid prevented or inh...

Membrane-bound ribosomes and messenger RNA remained associated with the microsomal membranes of human fibroblasts after cultures were treated with Verrucarin A, an inhibitor of initiation which led to extensive run-off of ribosomes from polysomal structures. When a membrane fraction from Verrucarin-treated cells containing such inactive ribosomes and mRNA was suspended in a medium of high salt ...

During early stages of cotranslational protein translocation across the endoplasmic reticulum (ER) membrane the ribosome is targeted to the heterotrimeric Sec61p complex, the major component of the protein-conducting channel. We demonstrate that this interaction is mediated by the 28S rRNA of the eukaryotic large ribosomal subunit. Bacterial ribosomes also bind via their 23S rRNA to the bacteri...

Radioactive amino acids were incorporated in vivo into N eurospora crassa cells, and the mitochondrial ribosomes were isolated. The incorporation of radioactivity into the proteins of these ribosomes was inhibited by cycloheximide, but not by chloramphenicol. It is therefore concluded that these proteins are synthesized on the cycloheximide sensitive and chloramphenicol insensitive cytoplasmic ...

Pokeweed antiviral protein (PAP) is a ribosome-inactivating protein that depurinates the highly conserved alpha-sarcin/ricin loop in the large rRNA. Here, using site-directed mutagenesis and systematic deletion analysis from the 5' and the 3' ends of the PAP cDNA, we identified the amino acids important for ribosome depurination and cytotoxicity of PAP. Truncating the first 16 amino acids of PA...

At both 4 and 24 hr after the administration of ethionine, female rats displayed a significant reduction in the RNA:pro tein ratio of liver microsomes. In this respect, ethionine behaved like many other hepatocarcinogens which induce ribosomal separation from the rough endoplasmic reticulum. This separation is usually brought about by the membrane, rather than ribosomal lesions. Using the disul...

Structural and genetic studies on prokaryotic ribosomes have provided important insights into fundamental aspects of protein synthesis and translational control and its interaction with ribosomal drugs. Comparable mechanistic studies in eukaryotes are mainly hampered by the absence of both high-resolution crystal structures and efficient genetic models. To study the interaction of aminoglycosid...

Treatment of synchronous cultures of Chlamydomonas reinhardtii with chloramphenicol at 4 hr after the beginning of the light phase led to a preferential loss of 70S ribosomes from the 17,000 x g(max) supernate. The "lost" 70S ribosomes were found associated with a thylakoid membrane fraction prepared from the 17,000 x g(max) pellet. Electron microscopic examinations of this fraction revealed th...

During conditions of nutrient deprivation, ribosomes are blocked by uncharged tRNA at the A site. The stringent factor RelA binds to blocked ribosomes and catalyzes synthesis of (p)ppGpp, a secondary messenger that induces the stringent response. We demonstrate that binding of RelA and (p)ppGpp synthesis are inversely coupled, i.e., (p)ppGpp synthesis decreases the affinity of RelA for the ribo...