The kinetics and thermodynamics of protein folding are commonly studied in vitro by denaturing/renaturing intact protein sequences. How these folding mechanisms relate to de novo folding that occurs as the nascent polypeptide emerges from the ribosome is much less well understood. Here, we have employed limited proteolysis followed by mass spectrometry analyses to compare directly free and ribo...

The journey of nascent polypeptides from synthesis at the peptidyl transferase center of the ribosome ("birth") to full function ("maturity") involves multiple interactions, constraints, modifications and folding events. Each step of this journey impacts the ultimate expression level and functional capacity of the translated protein. It has become clear that the kinetics of protein translation ...

The peripheral light-harvesting bacteriochlorophyll-carotenoid-protein complex B800-850 (LHII) has been isolated from membranes of semi-aerobic dark-grown cells of Rhodobacter sulfidophilus strain W4. A reversed-phase HPLC system resolved one beta- and one alpha-polypeptide in the ratio 1:1. The material obtained was of high purity and suitable for direct microsequence analysis. The primary str...

In yeast, the endoplasmic reticulum membrane proteins Sec11p and Spc3p are essential for the cleavage of signal peptides of nascent polypeptide chains during their passage through translocation sites. Genetic and biochemical experiments demonstrate that Sec11p and Spc3p are tightly associated with two other proteins, Spc1p and Spc2p, whose functions are largely unknown. Using anti-Spc2p antibod...

During heme deficiency in reticulocyte lysates, the heme-regulated translational inhibitor of protein synthesis (HRI) is activated and shuts off protein synthesis. In partial reactions, HRI phosphorylates the Mr 38,000 subunit (alpha subunit) of eukaryotic initiation factor 2 (eIF-2), which forms a ternary complex, Met-tRNAf X eIF-2 X GTP. The eIF-2 alpha (P) thus formed is not recognized by tw...

The signal recognition particle (SRP) recognizes polypeptide chains bearing a signal sequence as they emerge from the ribosome, and then binds its membrane-associated receptor (SR), thereby delivering the ribosome-nascent chain complex to the endoplasmic reticulum in eukaryotic cells and the plasma membrane in prokaryotic cells. SRP RNA catalytically accelerates the interaction of SRP and SR, w...

Ribosome stalling during translation can potentially be harmful, and is surveyed by a conserved quality control pathway that targets the associated mRNA and nascent polypeptide chain (NC). In this pathway, the ribosome-associated quality control (RQC) complex promotes the ubiquitylation and degradation of NCs remaining stalled in the 60S subunit. NC stalling is recognized by the Rqc2/Tae2 RQC s...

Nascent Polypeptide-associated Complex (NAC) was identified in eukaryotes as the first cytosolic factor which contacts the nascent polypeptide chain emerging from the ribosome. NAC is present as a homodimer in Archaea and as a highly conserved heterodimer in eukaryotes. Mutations in NAC cause severe embryonically lethal phenotypes in mice, D. melanogaster and C. elegans. In the yeast Saccharomy...