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Results for “Peptide Chain Initiation, Translational”

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PubMed1979

Interaction of a limited set of proteins with different mRNAs and protection of 5'-caps against pyrophosphatase digestion in initiation complexes.

A variety of 5'-3H-methyl-labeled, oxidized viral mRNAs were used as probes for detecting in wheat germ initiation complexes proteins that interact with, and can be cross-linked to, the 5'-cap structure. A limited and reproducible set of specific proteins was obtained with the different mRNAs. The binding of these proteins to the 5'-end of mRNA apparently results in protection against nucleotide pyrophosphatase digestion of the cap even in initiation complexes in which the 5'-end is susceptible to pancreatic RNase digestion. Cross-linked proteins from mammalian initiation complexes comigrated with several of the subunits of similarly treated eIF-3. A model for cap binding protein interaction with mRNA cap during initiation of translation is suggested.

Animals↗
PubMed1979

Differential effects of two interferon-induced translational inhibitors on initiation of protein synthesis.

At least two different mechanisms for the inhibition of mRNA translation operate in extracts of interferon-treated L cells. One is mediated by an interferon-induced protein kinase which, when activated by double-stranded RNA and ATP, phosphorylates the small subunit of initiation factor eIF-2. Addition of the purified interferon-induced protein kinase to L cell extracts, strongly reduces the amount of methionyl-tRNA bound to 40-S ribosomal subunits. The second translational inhibition is due to the synthesis of (2'-5')oligo(adenylate) by interferon-induced enzyme E. The oligonucleotide in turn activates a ribonuclease F constitutively present in L cells. Addition of the purified nuclease with its oligonucleotide activator to L cell extracts produces a strong decrease in polyribosome formation and an accumulation of initiation complex. These experiments differentiate the effects of the two interferon-induced inhibitors on mRNA translation.

Animals↗
PubMedDate not supplied

The role of acidic proteins from cytoplasmic fractions of Krebs II ascites cells for efficient translation.

Acidic proteins with affinity to RNA from cytoplasmic fraction of Krebs II Ascites cells were isolated by means of affinity chromatography on RNA-Sepharose CN-Br-columns. Stepwise elution with 350 mM [K+] and 1000 mM [K+] removed two fractions of proteins both of which are required for the formation of 40S- or 80S-initiation complexes and for efficient translation.

Animals↗
PubMed1979

Differential synthesis of lens proteins in the presence of m7G(5')pppG and cleavage product m7GMP in an embryonic chick lens cell lysate.

The effect of m7GMP release from m7GMP-containing mRNA cap sequence m7GpppG by the embryonic chick lens m7GpppN-pyrophosphatase activity on the synthesis of lens proteins was examined in a newly developed homologous translation system derived from 15-day embryonic chick lenses. The synthesis of total lens polypeptides and delta-crystallin polypeptides, the major translation product, was inhibited 84% and 88%, respectively, by 0.5 mM m7GpppG; m7GMP (0.5 mM) inhibited total synthesis by 63% but was 33% less inhibitory toward delta-crystallin synthesis; GpppG and GMP were not inhibitors, m7GpppG inhibited met-tRNAfmet incorporation into 80S initiation complexes.

Animals↗
PubMed1979

Further studies on the mode of action of the heme-controlled translational inhibitor.

We have isolated [de Haro, C. & Ochoa, S. (1978) Proc. Natl. Acad. Sci. USA 75, 2713-2716] a protein factor (eIF-2 stimulating protein, ESP) that is essential for formation of ternary and 40S initiation complexes by the eukaryotic polypeptide chain initiation factor 2 (eIF-2) at the low concentrations of eIF-2 present in reticulocyte lysates. The fact that stimulation of complex formation by ESP is virtually abolished when the small (38,000 daltons) subunit of eIF-2 is phosphorylated by ATP in the presence of eIF-2 kinase (heme-controlled inhibitor, HCI) is consistent with the notion that HCI inhibits translation in lysates by blocking the interaction of eIF-2 with ESP. Our present work, with highly purified eIF-2 and ESP, has additionally established that, unlike phosphorylation of the small subunit, phosphorylation of the middle (52,000 daltons) subunit of eIF-2, which does not lead to translational inhibition in lysates, does not affect eIF-2-ESP interaction. This provides further support for our model of translational inhibition by HCI.

Animals↗
PubMed1977

Partial characterization and proposed mode of action of inhibitory HeLa cell surface polypeptides.

Polypeptides removed from the HeLa cell surface by mild pronase treatment rapidly inhibit protein synthesis when added to HeLa cells or cell-free translation systems derived from HeLa cells. The inhibitory activity is heat stable. Protein and carbohydrate components of these polypeptides are required for inhibition of protein synthesis in vivo and in vitro. Two peaks of activity can be recovered from polyacrylamide gels, corresponding to polypeptides with molecular weights of approximately 29 000 and 41 000. Inhibition of protein synthesis in cell-free translation systems appears to be primarily an effect on elongation of polypeptide chains, whereas in the intact cell the primary target may be polypeptide chain initiation.

Cell-Free System↗
PubMed1979

Characterization of rabbit reticulocyte factor(s) that stimulates the translation of mRNAs lacking 5'-terminal 7-methylguanosine.

Purified reticulocyte initiation factors were assayed for their ability to stimulate the translation of uncapped vesicular stomatitis virus (VSV) mRNA relative to capped VSV mRNA in reticulocyte lysates. Both eIF-3 and eIF-4B preparations contained such an activity. However, at least some of the activity was due to the presence of an as yet unidentified factor that contaminated the eIF-3 and eIF-4B preparations. A polypeptide of apparent molecular weight 24,000 that can be specifically cross-linked to the oxidized 5'-terminal cap structures of reovirus and other viral mRNAs co-purifies with this new factor, and may be a component of it. This stimulatory activity present in our eIF-4B preparations was found to be greater when lower concentrations of KCl were present in the reaction mixture, possibly explaining why uncapped VSV mRNA is translated relatively more efficiently at low K+ concentrations.

Animals↗