Role of protein factor in the functional binding of ribosomes to natural messenger RNA

Initial dipeptide formation in hemoglobin biosynthesis

Initiation factors M(1) + M(2) from reticulocyte ribosomes bind Met-tRNA(F) to rabbit reticulocyte ribosomes containing endogenous hemoglobin mRNA. The initial binding of Met-tRNA(F) appears to be to the small ribosomal subunit. The Met-tRNA(F) is able to participate in what is presumed to be the first peptide bond in the formation of hemoglobin, namely the synthesis of a methionyl-valine dipeptide. The formation of this methionyl-valine dipeptide requires Met-tRNA(F), initiation factors M(1), M(2), and M(3), as well as Val-tRNA and T(1). No synthesis of methionyl-valine dipeptide takes place if Met-tRNA(F) is replaced by Met-tRNA(M), or if initiation factor M(3) is omitted. Thus, Met-tRNA(F) appears to be the initiator tRNA for hemoglobin biosynthesis and M(3), although required for the synthesis of the first peptide bond of hemoglobin, does not appear to be necessary, under the experimental conditions studied, for Met-tRNA(F) binding.

Ribosomal competence and spore germination in Fusarium solani

Extracts prepared from macroconidia of Fusarium solani f. sp. phaseoli are capable, under defined conditions, of incorporating phenylalanine into polypeptide with exogenous polyuridylic acid as messenger. Extracts from ungerminated and germinated spores have approximately the same activity. With endogenous template, leucine incorporation occurs, but in this reaction extracts from germinated spores have about 10 times more activity than do those from ungerminated spores. It is suggested that the low rate in ungerminated spores is attributable to a relative deficiency in the number of ribosomes which are organized into polysomes.

Reinitiation of RNA synthesis on transcription of chromatin DNA by Escherichia coli RNA polymerase

The transcription of DNA in chromatin by Escherichia coli RNA polymerase resembles that of isolated DNA in two important respects: the release of nascent RNA and reinitiation of RNA synthesis is dependent on the salt concentration, and RNA synthesis is markedly stimulated by the addition of ribosomes.

Formation of initiation complex with lambdamRNA in vitro

The product from the in vitro transcription of native lambdaDNA by purified E. coli RNA polymerase does not stimulate total amino acid incorporation although it can program ribosomes for the first peptide bond synthesis in the presence of the three initiation factor A, B and C.

Continued expression of the ribonucleic acid control gene during inhibition of Escherichia coli ribonucleic acid and protein synthesis

The effect of the ribonucleic acid (RNA) control (RC) gene on the biosynthesis of viral RNA has been examined in an RC(str) and an RC(rel) host infected with R17 RNA bacteriophage under conditions in which host RNA and protein synthesis were inhibited by the addition of rifampicin. Methionine and isoleucine starvation depressed viral RNA biosynthesis in an RC(str) host but not in an RC(rel) host. However, histidine starvation had little effect on viral RNA and protein synthesis in both RC(str) and RC(rel) cells, although it had a marked effect on host protein and RNA synthesis in an RC(str) host. Chloramphenicol relieved the effect of amino acid starvation on viral RNA synthesis in an RC(str) host. It is concluded that stringent control of viral RNA biosynthesis does not require the continued biosynthesis of the RC gene product (RNA or protein) and that a preformed RC gene product can regulate the biosynthesis of the exogenous RNA. It is suggested that the amino acid dependence of viral RNA biosynthesis is due to its obligatory coupling with the translation of the viral coat protein which lacks histidine. It may be inferred that the amino acid requirement of bacterial RNA is due to its coupling with the translation of a host-specific protein (other than the RC gene product) which requires a full complement of amino acids. Since chloramphenicol is known to permit ribosome movement in the absence of protein synthesis, it is suggested that ribosome movement along the nascent RNA chain is a sufficient condition for the continuation of RNA synthesis.

Aurintricarboxylic acid and initiation factors of wheat embryo

In extracts of wheat embryo, aurintricarboxylic acid inhibits attachment of ribosomes to messenger RNA and has little effect on aminoacyl transfer to peptide. This specificity of inhibition allows (i) the demonstration that the initial phase of amino acid incorporation dependent on RNA of tobacco mosaic virus involves an "initiation" reaction between ribosome and messenger RNA which requires two soluble factors, (ii) an assay facilitating purification of the initiation factors, and (iii) the demonstration that these factors are distinct from aminoacyl transfer enzymes.

An initiation factor causing dissociation of E. coli ribosomes

Purification of crude initiation factors, essential for polypeptide synthesis in cell-free systems of E. coli, yielded a fraction DF which causes dissociation of 70 S ribosomes. Its stoichiometric action on 70 S ribosomes is antagonized by increasing Mg(2+) concentrations but not by the addition of 30 S and 50 S subunits washed with high salt concentration. GTP did not stimulate this dissociating action. 2 &mgr;g of our most purified preparation caused 100% dissociation of 100 &mgr;g of 70 S ribosomes without added GTP. DF-induced dissociation is a very rapid process at 37 degrees C and is temperature-dependent in the range of 0 degrees -37 degrees C. DF, which is thermolabile factor, is much less or not effective with complexed 70 S ribosomes bearing peptidyl-tRNA and mRNA.

Studies on a nucleoprotein prepared from rat liver polysomes by digestion with T1 ribonuclease

1. Treatment of rat liver polysomes in a buffer containing 2.5mm-magnesium chloride with T(1) ribonuclease at a concentration of 330units/ml. of reaction medium at 37 degrees for 2hr. leads to the production of an insoluble nucleoprotein. 2. On the bases of analysis for protein and RNA and of u.v.-absorption spectra the nucleoprotein appears to have lost approx. 60% of the structural RNA originally present in the ribosome. Degradation of (3)H-labelled polysomes (structural RNA labelled with orotic acid) with T(1) ribonuclease leads to nucleoprotein preparations retaining approx. 30% of the radioactivity originally present in the polysomes. By means of sucrose-density-gradient centrifugation it is shown that the nucleoprotein preparations are free of single 73s ribosomes and ribosomal subunits. No evidence for the presence of 28s and 18s structural RNA was obtained on examination of extracted nucleoprotein-particle RNA by means of sucrose-density-gradient centrifugation. 3. Digestion of washed polysomes carrying (14)C-labelled nascent peptide chains with T(1) ribonuclease gives a nucleoprotein particle that retains approx. 70% of the original labelled chains. Treatment of labelled nucleoprotein particles with 1mm-puromycin in the absence of transfer factors releases 20% of the labelled chains. Addition of GTP (0.48mumole) increases this release to 37%. 4. Treatment of nucleoprotein particles carrying (14)C-labelled peptide chains with either EDTA (50mm) or ammonium chloride (0.5m) brings about a small release of labelled material (approx. 15%). 5. Disruption of nucleoprotein particles carrying (14)C-labelled peptide chains with either sodium dodecyl sulphate or 2m-lithium chloride, followed by addition of transfer RNA as marker and chromatography on Sephadex G-200, show in both cases that considerable amounts of labelled peptide material move well ahead of the added transfer RNA marker. Further, if nucleoprotein particles carrying labelled peptide chains are treated with 0.3m-potassium hydroxide at 20 degrees for 24 hr., neutralized to pH7.6, and then chromatographed on Sephadex G-200, the labelled peptide material moves much closer to the added transfer RNA marker. These results suggest that a proportion of the nascent (14)C-labelled peptides on the nucleoprotein are attached to transfer RNA or large fragments of transfer RNA. 6. [(3)H]Polyuridylic acid binds to nucleoprotein particles in 1mm-magnesium chloride. The rate of binding is rapid when measured at 20 degrees .

On the mechanism of action of adrenocorticotropic hormone: the binding of cyclic-3',5'-adenosine monophosphate to an adrenal cortical protein

The binding of cyclic 3',5'-adenosine monophosphate (cyclic AMP) within the adrenal cortical cell was studied. Cyclic AMP binds specifically to a protein which is associated predominantly with the microsomal fraction of the cell. The binding protein was purified approximately 100-fold.

A factor that stimulates RNA synthesis by purified RNA polymerase

A protein factor, partially purified from E. coli, can stimulate some 30- to 50-fold the transcription of DNA by purified RNA polymerase. Evidence is presented suggesting that this stimulatory factor (designated M factor) exerts its effect before the RNA synthesis is initiated. The M factor is prepared from a crude ribosome fraction, but it does not require the presence of ribosomes for full activity.