Protein synthesis in rabbit reticulocytes. Purification and characterization of a double-stranded RNA-dependent protein synthesis inhibitor from reticulocyte lysates

Reticulocyte lysates contain a latent form of eukaryotic peptide chain initiation factor 2 (eIF-2) kinase (dsI) which becomes activated in the presence of double-stranded RNA and ATP and inhibits protein synthesis. The latent form of dsI has been partially purified from reticulocyte ribosomal salt wash. The purified dsI has been activated by incubation in the presence of poly(rI).poly(rC) and [gamma 32P]ATP and the activated dsI has been further purified to near homogeneity. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, purified [32P]dsI shows an intensely staining 67,000-dalton polypeptide band which corresponds to a single 67,000-dalton radioactive band. During Sephadex (G-200) gel filtration, both the latent form of dsI and the activated dsI elute similarly with a peak corresponding to a molecular weight of 67,000. Purified dsI phosphorylates the 38,000-dalton subunit of eIF-2 and, under conditions of eIF-2 phosphorylation, dsI strongly inhibits AUG-dependent Met-tRNAf binding to 40 S ribosomes. Also, in partial reactions, eIF-2 alpha (P) formed by phosphorylation of eIF-2 using dsI and ATP, is not recognized by two eIF-2 ancillary factors, Co-eIF-2B and Co-eIF-2C. These results are similar to those reported previously for the heme-regulated eIF-2 kinase (Das, A., Ralston, R. O., Grace, M., Roy, R., Ghosh-Dastidar, P., Das H. K., Yaghmai, B., Palmieri, S., and Gupta, N. K. (1979) Proc. Natl. Acad. Sci. U. S. A. 76,5076-5079) and suggest that dsI, like the heme-regulated eIF-2 kinase phosphorylates eIF-2 and eIF-2 alpha (P) thus formed, in both cases, is not recognized by Co-eIF-2B and Co-eIF-2C, and is inactive in some step(s) of Met-tRNAf.40 S initiation complex formation.

Efficacies of vaccines against canine hookworm disease

Three types of vaccine (1) a sonicated extract of killed larvae, (2) 5-fluorouracil-treated larvae and (3) 40 krad. X-irradiated larvae have been evaluated. Pups aged 3-4 months, weighing 2 +/- 0.5 kg and free of natural hookworm infection were selected for experimental studies. The sonicated extract was given either in a single dose or as 2 doses at weekly intervals, whereas the 5-fluorouracil-treated and X-irradiated larvae were given in a single dose only. After completion of the vaccination schedule, the pups were challenged with filariform larvae and were sacrificed 3 weeks after challenge. Non-vaccinated pups and those vaccinated with a single dose of sonicated extract lost weight and had diarrhoea or dysentery after challenge. Furthermore, in non-vaccinated pups, haemoglobin levels fell and at autopsy the intestinal mucosa was found to be grossly congested and free blood was present in the lumen of the intestine. Such findings were not obtained in pups vaccinated with the other types of vaccines. The percentage of infective larvae which developed to the adult stage in non-vaccinated pups was 82.7 +/- 9.53 compared with 45.1 +/- 12.33, 30.1 +/- 10.05, 20.6 +/- 10.60 and 8.0 +/- 7.46%, respectively in pups vaccinated with a single dose of sonicated extract, double dose of sonicated extract, 5-fluorouracil-treated and 40 krad. X-irradiated larval vaccines. While the irradiated larval vaccine provided maximum protection against clinical ancylostomiasis, 2 doses of the sonicated larval vaccine could also afford almost equal protection to pups.

Protein synthesis in rabbit reticulocytes. Co-eIF-2A reverses mRNA inhibition of ternary complex (Met-tRNAf.eIF-2.GTP) formation by eIF-2

mRNAs, at low concentrations, drastically inhibit ternary complex formation by eIF-2 (Met-tRNAf.eIF-2.GTP) and, when added to the preformed ternary complex, cause extensive dissociation of the complex. Co-eIF-2A stimulates (2- to 4-fold) Met-tRNAf binding to eIF-2 and, in the presence of excess Co-eIF-2A, the stimulated Met-tRNAf binding to eIF-2 is fully resistant to mRNAs. Other cofactors tested such as Co-eIF-2B and Co-eIF-2C do not reverse mRNA inhibition of ternary complex formation.

Protein synthesis in rabbit reticulocytes. Preparation of homogeneous Met-tRNAf deacylase and studies of its role in protein synthesis

Met-tRNAf deacylase from reticulocyte ribosomes has been purified to homogeneity. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the homogeneous preparation gives a single protein band corresponding to a molecular weight of approximately 67,000. Purified Met-tRNAf deacylase degrades free Met-tRNAf and also Met-tRNAf bound to 40 S ribosomes in the presence of AUG codon but does not degrade Met-tRNAf in the ternary complex, Met-tRNAf.eIF-2.GTP. Purified Met-tRNAf deacylase does not inhibit protein synthesis in reticulocyte lysates at any concentration tested indicating that Met-tRNAf deacylase is not a protein synthesis inhibitor. Antibodies against Met-tRNAf deacylase have been prepared by immunizing a chicken with homogeneous preparation of Met-tRNAf deacylase. Addition of anti-Met-tRNAf deacylase does not have any effect on protein synthesis in reticulocyte lysates indicating that Met-tRNAf deacylase is not required for protein synthesis.

Protein synthesis in rabbit reticulocytes. A study of the mechanism of interreaction of fluorescently labeled co-eIF-2A with eIF-2 using fluorescence polarization

5-Dimethylaminonaphthalene-1-sulfonyl (dansyl)-Co-eIF-2A was prepared using homogeneous Co-eIF-2A. Dansyl-Co-eIF-2A was as active as untreated Co-eIF-2A when assayed for stimulation of ternary complex formation and also for protection of the ternary complex from dissociation by aurintricarboxylic acid. The mechanism of interaction of dansyl-Co-eIF-2A with eIF-2 was studied by measuring changes in fluorescence polarization. These studies indicate that dansyl-Co-eIF-2A interacts specifically with the ternary complex and does not interact with free eIF-2 or with two other high molecular weight protein complexes, Co-eIF-2B and Co-eIF-2C. Mg2+ inhibits ternary complex formation by eIF-2 and Co-eIF-2C relieves this Mg2+ inhibition of ternary complex formation. In both cases, the changes in fluorescence polarization of dansyl-Co-eIF-2A correlate well with the extent of ternary complex formed.

Protein synthesis in rabbit reticulocytes. Demonstration of the requirements for eIF-2 and Co-eIF-2A for peptide chain initiation using immune sera

Antisera to eIF-2 and Co-eIF-2A have been prepared by immunizing two chickens separately with homogeneous preparations of either eIF-2 or Co-eIF-2A. Addition of anti-eIF-2 or anti-Co-eIF-2A to reticulocyte lysates strongly inhibits protein synthesis and, in each case, protein synthesis inhibition is reversed by the addition of the corresponding homogeneous factor. Protein synthesis inhibition by anti-Co-eIF-2A is not reversed by eIF-2 at any concentration tested indicating an absolute requirement for Co-eIF-2A in protein synthesis. Also, in partial peptide chain initiation reactions, the addition of anti-Co-eIF-2A inhibits Co-eIF-2A stimulation of ternary complex formation by eIF-2 and Co-eIF-2A protection of ternary complexes in the presence of aurintricarboxylic acid.

Protein synthesis in rabbit reticulocytes: characteristics of a postribosomal supernatant factor that reverses inhibition of protein synthesis in heme-deficient lysates and inhibition of ternary complex (Met-tRNAfMet.eIF-2.GTP) formation by heme-regulated inhibitor

During heme deficiency in reticulocyte lysates, a translational inhibitor (heme-regulated inhibitor, HRI) that blocks polypeptide chain initiation is activated. HRI is a protein kinase that specifically phosphorylates the 38,000-dalton subunit of the Met-tRNAfMet binding factor, eIF-2. Phosphorylation of eIF-2 by HRI prevents its interaction with at least two additional factors, resulting in a net reduction in formation of ternary complex (Met-tRNAfMet.eIF-2.GTP) and AUG-dependent transfer of Met-tRNAfMet to 40S ribosomal subunits. A factor (sRF) that reverses protein synthesis inhibition in heme-deficient lysates has been purified from reticulocyte postribosomal supernatant. sRF also reverses the inhibition of ternary complex formation by HRI in a fractionated system. The ternary complex inhibition reversal activity and the protein synthesis inhibition reversal activity cosediment at 12.5 S upon glycerol density gradient centrifugation, and both activities are sensitive to heat or N-ethylmaleimide. Purified sRF does not dephosphorylate eIF-2 whose phosphorylation has been catalyzed by HRI, nor does the sRF prevent the phosphorylation of eIF-2 by HRI in a fractionated system. sRF stimulates ternary complex formation by both phosphorylated and nonphosphorylated eIF-2. These observations suggest that the sensitivity of protein synthesis to phosphorylation of eIF-2 by HRI may be modulated by the concentration and activity of sRF.

Protein synthesis in rabbit reticulocytes: mechanism of protein synthesis inhibition by heme-regulated inhibitor

Partially purified Met-tRNAf binding factor, eIF-2, was phosphorylated by using heme-regulated inhibitor (HRI). Phosphorylated eIF-2 was freed from HRI by phosphocellulose column chromatography. Analysis by isoelectric focusing showed 100% phosphorylation of the 38,000-dalton subunit of eIF-2. Both eIF-2 and eIF-2(P) formed ternary complexes with Met-tRNAf and GTP with almost the same efficiency, and in both cases the ternary complex formation was drastically inhibited by prior addition of Mg2+. However, whereas the ternary complexes formed with eIF-2 could be stimulated by Co-eIF-2C at 1 mM Mg2+ and dissociated by Co-eIF-2B at 5 mM Mg2+, the ternary complexes formed with eIF-2(P) were unresponsive to both Co-eIF-2B and Co-e-IF-2C. Also, under conditions of eIF-2 phosphorylation, HRI drastically inhibited AUG-dependent Met-tRNAf binding to 40S ribosomes. However, HRI (in the presence of ATP) had no effect on the joining of preformed Met-tRNAf . 40S . AUG complex to the 60S ribosomal subunit to form Met-tRNAf-80S . AUG complex. These studies suggest that HRI inhibits protein synthesis initiation by phosphorylation of the 38,000-dalton subunit of eIF-2. HRI-phosphorylated eIF-2 does not interact with at least two other protein factors, Co-eIF-2B and Co-eIF-2C, and is thus inactive in protein synthesis initiation.

Protein synthesis in rabbit reticulocytes: characteristics of a ribosomal factor that reverses inhibition of protein synthesis in heme-deficient lysates

A ribosomal salt (0.5 M KCl) wash factor (RF) that reverses inhibition of protein synthesis in heme-deficient reticulocyte lysates has been resolved from the bulk of Met-tRNAfMet-binding factor (EIF-1), Co-EIF-1, and EIF-2 (ternary complex dissociation factor, TDF). The purified RF restores protein synthesis activity of heme-deficient lysates to the level observed in the presence of hemin. No direct correlation exists between amount of EIF-1 activity and ability to reverse inhibition of protein synthesis in heme-deficient lysates. Homogeneous preparations of EIF-1 are completely inactive in reversal of protein synthesis inhibition in heme-deficient lysates. These findings suggest that RF activity is not due to EIF-1 alone but may or may not require EIF-1 as a component of a complex factor.

Protein synthesis in rabbit reticulocytes XXI. Purification and properties of a protein factor (Co-EIF-1) which stimulates Met-tRNAf binding to EIF-1

The peptide chain initiation factor, Co-EIF-1 has been purified to homogeneity. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the homogeneous preparation gives a single protein band corresponding to a molecular weight of approximately 20,000. In the crude preparation, Co-EIF-1 exists in two molecular forms: Co-EIF-1H (Mr = 200,000) and Co-EIF-1L (Mr = 20,000). Both forms are equally active in all the reactions studied. Upon heating, the heavy form (Co-EIF-1H) is completely converted into the light form (Co-EIF-1L). Radioactively labeled [14C]Co-EIF-1 was prepared by reductive alkylation using [14C]formaldehyde and borohydride. [14C]Methyl-Co-EIF-1 binds specifically to EIF-1; EIF-1.[14C]Co-EIF-1 complex was analyzed by gel (Sephadex G-100) filtration. EIF-1.Co-EIF-1 complex is distinctly more stable towards heat than EIF-1 alone and the quarternary complex, Met-tRNAf.EIF-1.Co-EIF-1.GTP is more resistant to aurintricarboxylic acid than the ternary complex, Met-tRNAf.EIF-1.GTP. Both the quarternary complex, Met-tRNAf.EIF-1.Co-EIF-1.GTP, and the ternary complex, Met-tRNAf.EIF-1.GTP, are equally sensitive to Mg2+ in the presence of EIF-2 (TDF). In the presence of Co-EIF-1, the initial rate of Met-tRNAf binding to 40 S ribosomes was significantly increased.

Regulation of protein synthesis in rabbit reticulocyte lysates by the heme-regulated protein kinase: inhibition of interaction of Met-tRNAfMet binding factor with another initiation factor in formation of Met-tRNAfMet.40S ribosomal subunit complexes

Protein synthesis in reticulocytes and their lysates is regulated by heme. In heme deficiency a heme-regulated translational inhibitor (HRI) that blocks initiation of polypeptide chains is activated. HRI is a protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) that specifically phosphorylates the 38,000-dalton subunit of the Met-tRNA(f) (Met) binding factor (IF), which forms a ternary complex with Met-tRNA(f) (Met) and GTP, a finding that suggests that the inhibition by HRI involves the phosphorylation of IF. We have investigated the effect of HRI in the partial reactions of protein chain initiation in which the IF-promoted binding of Met-tRNA(f) (Met) to 40S ribosomal subunits is enhanced by another initiation factor [ternary complex dissociation factor (TDF)] and AUG. The results show that HRI at very low concentrations markedly inhibits the binding of Met-tRNA(f) (Met) to 40S subunits. The inhibitory effect of HRI requires ATP. Under these conditions HRI phosphorylates only the 38,000-dalton subunit of IF. The TDF preparations not only promote the binding of the ternary complex to 40S subunits but also promote the dissociation of the ternary complex in the presence of 5 mM Mg(2+) at 0 degrees . The preincubation of purified IF alone with low concentrations of HRI and ATP does not significantly affect its capacity to form the ternary complex; however, the TDF-promoted dissociation of the ternary complex is inhibited. The nonhydrolyzable analog adenosine 5'-[beta,gamma-imido]triphosphate does not substitute for ATP. These findings suggest that phosphorylation causes a conformational modification in IF, which results in inhibition of the interaction between the ternary complex and TDF that is required for the binding of the ternary complex to 40S subunits.

Protein synthesis in rabbit reticulocytes. Characteristics of mRNA (AUG codon)-dependent binding of Met-tRNAfMet to 40 S and 80 S ribosomes

The characteristics of Met-tRNAfMet binding to ribosomes (40 S and 80 S) were studied using a two-stage assay method (Gupta, N.K., Chatterjee, B. and Majumdar, A. (1975) Biochem. Biophys. Res. Commun. 65, 797) and the complexes formed were analyzed either by Millipore filtration or by sucrose density gradient centrifugation. The results are summarized as follows: (a) with both assay methods, Met-tRNAfMet binding to 40 S ribosomes was entirely dependent upon addition of a partially purified mixture of initiation factors and AUG codon; (b) this binding occurred over a wide Mg2+ concentration range; significant binding was observed even at 20 mM Mg2+; (c) upon addition of 60 S ribosomes, a significant part of Met-tRNAfMet bound to 40 S ribosomes was transferred to 80 S complex. This transfer reaction had a sharp Mg2+ optimum around 2 mM. Met-tRNAfMet-80 S-AUG complex thus formed was active in Met-puromycin synthesis; (d) Met-tRNAfMet deacylase present in crude 0.5 M KCl ribosomal wash is a potent inhibitor of the binding reaction as it deacylates Met-tRNAfMet in the Met-tRNAfMet-40 S-AUG complex; (e) glutaraldehyde (0.5%) degrades Met-tRNAfMet-40 S-AUG complex but increases the background binding of Met-tRNAfMet to 40 S ribosomes in the absence of AUG codon; (f) polynucleotides containing uracil and adenosine are strong inhibitors of Met-tRNAfMet binding to 40 S ribosomes. The order of inhibitory activities of the polynucleotides tested was as follows: poly(rU)-poly(rA) (2:1) greater than poly(rU)-poly(rA) (1:1) greater than poly(rU) greater than poly(rA). Other RNAs tested such as poly(rC), poly(rI)-poly(rC) and phi6 bacteriophage RNA (double-stranded) were without significant effects on the Met-tRNAfMet-binding reaction.

Specific binding of Excherichia coli chain Initiation factor 2 to fMet-tRnafMet

A stable Escherichia coli IF-2-fMet-tRNAfMet complex is formed upon incubation of IF-2 (prokaryotic initiation factor) with fMet-tRNAfMet is the presence of 50 mM Tris-HCl, pH 7.0, 100 mM NH4Cl, and 7 mM 2-mercaptoethanol. The complex thus formed is retained on a Millipore filter and is assayed accordingly. Complex formation does dot require GTP, is unstable in the presence of 5 mM Mg2+, and is specific for fMet-tRNAfMet. Other amino acyl-tRNAs or deacylated tRNAs do not form such a complex with IF-2. A crude ribosomal high salt wash preparation contains other protein factors which bind unspecifically to RNAs under the above binding conditions. One of these factors elute similarly to IF-1 on DEAE-cellulose chromatography. Extensively purified IF-1 and IF-3 show weak and unspecific RNA-binding activities. The RNA-protein complex formed in each of the above cases, like the IF-2-fMet-tRNAfMet complex, is retained on Millipore filter and is sensitive to Mg2+.

A preliminary study of iron absorption by whole body counting and correlation with DFO excretion

A preliminary study of iron absorption by whole body counting was carried on a group of 16 women. The cases included 8 patients suffering from iron deficiency anaemia and various infections as well as 8 healthy controls. High iron absorption is associated with iron deficiency, these changes being more marked in iron deficient controls than in those with infection or malignancy. In iron deficient controls results of whole body counting correlate very well with other haematological investigations.

Protein synthesis in rabbit reticulocytes. A study of Met-tRNA f Met binding factor(s) and Met-tRNA f Met binding to ribosomes and AUG codon

The effects of additions of Mg-2+, ribosomes, and AUG codon on the Met-tRNAf Met-initiation factor-GTP complex were studied using a Millipore filtration method (J. Biol. Chem. 248, 4500 (1973)). Upon addition of increasing concentration of Mg-2+, the Met-tRNAf Met-initiation factor-GTP complex dissociates into free Met-tRNAf Met and initiation factor (GTP), with an infection around 1.5 to 2 mM Mg-2+. The Mg-2+-induced dissociation of Met-tRNAf Met-initiation factor-GTP complex was enhanced at ice bath temperature. At 37 degrees and in the presence of 1.5 to 2mM Mg-2+, the Met-tRNAf Met-initiation factor-GTP complex catalyzes the transfer of Met-tRNAf Met to ribosomes and AUG codon. Ribosome bound Met-tRNAf Met is stable to Mg-2+ and low temperature. A Millipore filtration assay for studies of (35S)Met-tRNAf Met binding to ribosomes and Aug codon has been developed. The assay procedure is carried out in three stages. In Stage I, the Met-tRNAf Met is bound to initiation factor in the presence of GTP, AUG codon (required for Stage II reaction), and 3.7 times 10-5 M aurintricarboxylic acid. The incubation is carried out at 37 degrees for 5 min. In Stage II, ribosomes and Mg-2+ (1.5 to 2mM final concentration) are added and the incubation is continued at 37 degrees for 10 min. In Stage III, more Mg-2+ is added to make the final Mg-2+ concentration of the incubation mixture 5 mM, and the reactions are further incubated at ice bath temperature for 10 min. The reactions are then terminated by addition of excess cold wash buffer and filtered through Millipore filters. Under the standard assay conditions, the radioactivity bound to Millipore filters in the absence of ribosomes and AUG codon is markedly reduced. Addition of ribosomes alone gave a significant increase in the radioactivity bound to Millipore filters. A further 2- to 3-fold stimulation of binding of (35S)Met-tRNAf Met to Millipore filters was observed when both ribosomes and AUG codon were added. The Met-tRNAf Met bound to ribosomes under the assay condition was reactive with puromycin. Upon DEAE-cellulose chromatography of a partially purified mixture of initiation factors (IF), Met-tRNAf Met binding activities separate into two forms, and are designated as IF-1A and IF-1B. These two forms can be distinguished by the stabilities of their respective Met-tRNAf Met-IF-1-GTP complexes to Mg-2+. The Met-tRNAf Met-IF-1A-GTP complex is distinctly more stable in the presence of Mg-2+ than Met-tRNAf Met-IF-1B-GTP complex. Continue.