Nascent polypeptides

Baler, R., Welch, W.J., Voellmy, R. (1992). Heat shock gene regulation by nascent polypeptides and denatured proteins hsp70 as a potential autoregulatory factor. J. Cell. Biol. 117, 1151-1159. 

After mRNA splicing, the tropoelastin mRNA is translated at the surface of the rough endoplasmic reticulum (RER) in a variety of cells smooth muscle cells, endothelial and microvascular cells, chondrocytes and fibroblasts. The approximately 70 kDa precursor protein (depending on isoform) is synthesized with an N-terminal 26-amino-acid signal peptide. This nascent polypeptide chain is transported into the lumen of the RER, where the signal peptide is removed cotranslationally [9]. 

DNA sequencing reveals the order in which amino acids are added to the nascent polypeptide chain as it is synthesized on the ribosomes. However, it provides no information about posttranslational modifications such as proteolytic processing, methylation, glycosylation, phosphorylation, hydroxylation of prohne and lysine, and disulfide bond formation that accompany mamra-tion. While Edman sequencing can detect the presence of most posttranslational events, technical hmitations often prevent identification of a specific modification. 

Deformylation of nascent polypeptides has been shown to be a function essential for growth in E. coli, Staphylococcus aureus and Streptococcus pneumoniae [15-18]. Moreover, antibacterial mode of action studies, using S. pneumoniae or S. aureus strains in which the expression of PDF is controlled by regulatable promoters, have shown that the antibacterial activity of PDF inhibitors is due to their inhibition of the PDF enzyme, as the susceptibility of the strains to these compounds is dependent on the amount of protein present in the cell [19-21]. These results further validate PDF as a target for novel antibiotics. 

Antony, A. C., and Miller, M. E. (1994). Statistical prediction of the locus of endoproteo-lytic cleavage of the nascent polypeptide in glycosylphosphatidylinositol-anchored proteins. Biochem. J. 298, 9-16. 

Beatrix, B., Sakai, H., and Wiedmann, M., The alpha and beta subunit of the nascent polypeptide-associated complex have distinct functions, J. Biol Biol, 2000, 275, 37838. 

We have shown that out of fifteen forms of three-dimensional crystals from ribosomal particles, grown so far in our laboratory, some appear suitable for crystallographic data collection when using synchrotron radiation at temperatures between 19 °C and —180 °C 50S subunits from H. marismortui., and from B. stearothermophilus, including the -BLl 1 mutant, and the new crystal forms from B. stearothermophilus SOS and Thermus thermophilus 30S subunits which have only recently been grown in non-volatile precipitants We also plan to continue research on biochemically modified particles, such as SOS with one tRNA and its nascent polypeptide chain (which have already been crystallized). 

Gautschi M, Just S, Mun A, Ross S, Riicknagel P, Dubaquie Y, Ehrenhofer-Murray A, Rospert S (2003) The yeast Na-acetyltransferase NatA is quantitatively anchored to the ribosome and interacts with nascent polypeptides. Mol Cell Biol 23 7403-7414... 

Rospert S (2004) Ribosome function how to govern the fate of a nascent polypeptide. Curr Biol 14 R386-R388... 

FIGURE 5.1(b) Biosynthetic processing of A -glycans in the plant ER and Golgi. Each step indicates the glycosyl groups added to or modified on a nascent polypeptide and the enzymes responsible for this process. (Revised from Chen et al. (2005). Med. Res. Rev. 25(3), 343-360.)... 

The biological function of this dolichol-linked oligosaccharide was revealed in pulse-chase experiments which showed that the intact oligosaccharide was transferred, as such, to protein. Subsequent studies, to be discussed, confirmed that the formation of the oligosaccharide linked to the Asn residues of glycoproteins is probably initiated by transfer of the oligosaccharide from the dolichol diphosphate intermediate to the asparagine residue of a nascent polypeptide (see Refs. 35, 49, 50, and 67 for reviews). 

FIGURE 27-26 Termination of protein synthesis in bacteria. Termination occurs in response to a termination codon in the A site. First, a release factor, RF (RF-1 or RF-2, depending on which termination codon is present), binds to the A site. This leads to hydrolysis of the ester linkage between the nascent polypeptide and the tRNA in the P site and release of the completed polypeptide. Finally, the mRNA, de-acylated tRNA, and release factor leave the ribosome, and the ribosome dissociates into its 30S and 50S subunits. 

FIGURE 27-33 Directing eukaryotic proteins with the appropriate signals to the endoplasmic reticulum. This process involves the SRP cycle and translocation and cleavage of the nascent polypeptide. The steps are described in the text. SRP is a rod-shaped complex containing a 300 nucleotide RNA (7SL-RNA) and six different proteins (combined Mr 325,000). One protein subunit of SRP binds directly to... 

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