Preparation and characteristics of a wheat embryo cell-free extract active in the synthesis of high molecular weight viral polypeptides

Characterisation of synthetic DNA probe detecting potato spindle tuber viroid

Chemically synthesized DNA fragments complementary to selected regions of the potato spindle tuber viroid (PSTV) genome were cloned into Escherichia coli plasmid pUC9. One of the recombinant plasmids (pIBB4) with a 87 bp insert representing the central region of the PSTV genome (nucleotides 88 to 174) was used after labelling by nick translation for detecting PSTV by dot-blot hybridization. The molecular probe was almost as sensitive as the one carrying the full genomic PSTV copy (pAV401), detecting down to 20 pg of PSTV RNA in 8-15 micrograms of infected tissue. The specificity of the test was high; no signals were created by extracts from healthy plants or plants infected with a variety of common potato viruses. The probe is potentially useful in studies on mixed infections of potatoes with different viruses, and in selection of certified seed material.

A reverse transcriptase-like activity of wheat (Triticum aestivum) embryo microsomal fraction

A reverse transcriptase-like activity was isolated from germinating wheat (Triticum aestivum) embryos. The activity was found to be associated with a microsomal fraction (70,000 g pellet) of the embryo homogenate. The microsome-associated enzyme prefers homologous polyadenylated RNA to any other polynucleotides as template and requires all four deoxyribonucleoside triphosphates for maximal activity. The reaction product appears in the incubation mixture in the form of an RNA-DNA hybrid, which can be converted into single-stranded DNA by mild alkaline hydrolysis. These observations suggest that normal wheat embryo cells contain an enzyme which, functionally, is similar to retroviral reverse transcriptase.

Intracellular coding sites of polypeptides associated with photosynthetic oxygen evolution of photosystem II

Three hydrophilic polypeptides of approximately 34, 23, and 16 kd located on the inner thylakoid surface are associated with the water-splitting activity of photosystem II. Stable transcripts for the three proteins were found only in cytosolic (polyadenylated) RNA, suggesting that they are encoded in nuclear genes. The immunologically reacting products synthesized in a rabbit reticulocyte cell-free translation system are larger in size than the authentic mature proteins by about 6-10 kd. These larger precursors are imported post-translationally into isolated, intact chloroplasts, and are processed to their mature forms during or after translocation. The imported proteins can be extracted from thylakoids by procedures used to isolate the three native proteins of the water-splitting complex, suggesting that they have assembled properly into their final destination, the inner thylakoid surface.

Reproducible preparation of a wheat germ cell-free system

This study has examined whether the conditions used for the precipitation of plant mRNPs are suitable for the reduction of endogenous template activity in the wheat germ cell-free system. These results have led to a modification of the procedure for the preparation of the wheat germ system that allows the consistent preparation of an active in vitro translation system with low endogenous activity.

Secretion of plant storage globulin polypeptides by Xenopus laevis oocytes

Xenopus oocytes injected with poly(A)-containing RNA from developing cotyledons of field beans (Vicia faba L. var. minor) synthesize precursor polypeptides to the major storage globulins legumin and vicilin. These polypeptides are secreted into the medium without proteolytic cleavage of the legumin propolypeptides into the mature disulfide-linked alpha and beta chains. Similarly, storage globulin polypeptides from pea (Pisum sativum L.) and french bean (Phaseolus vulgaris L.) were secreted from oocytes. Inhibition of glycosylation by tunicamycin does not prevent secretion. This first report on the secretion of plant polypeptides by Xenopus oocytes shows that (a) intracellular deposition of storage proteins in membrane-bounded organelles (protein bodies) of plants and extracellular secretion have step(s) in common, and (b) the cell, in addition to the mRNA, determines the final destination of these polypeptides.

In vitro synthesis of polypeptides of moderately large size by poly(A)-containing messenger RNA from postmortem human brain and mouse brain

Studies were undertaken to optimize the conditions for isolation and in vitro translation of poly(A)-containing mRNA from human postmortem brain. The comparison of several methods for preparation of mRNA from frozen mouse brain indicated that although the yield of mRNA was increased using polysomes prepared in the presence of ribonucleoside vanadyl complexes and subsequently extracted with guanidinium thiocyanate, the translation products were indistinguishable from those synthesized by total cellular RNA directly extracted from tissue with guanidinium thiocyanate. The oligo d(T)-cellulose-purified poly(A)-containing mRNA preparations were translated in vitro in a rabbit reticulocyte lysate in the presence of L-[35S]methionine. Messenger RNA from frozen mouse brain stimulated protein synthesis from 9- to 20-fold over endogenous mRNA. Over 450 polypeptides were reproducibly synthesized and separated by two-dimensional polyacrylamide gel electrophoresis (PAGE); size classes up to 130,000 daltons were present. Direct extraction of RNA from frozen human cerebral cortex and cerebellum with guanidinium thiocyanate followed by oligo d(T)-cellulose chromatography yielded 1.8 micrograms/g and 2.0 micrograms/g, respectively, of poly(A)-containing mRNA; this represents a two- to fourfold increase over our earlier results. In the rabbit reticulocyte translation system human brain mRNA stimulated protein synthesis nearly threefold over endogenous mRNA. Compared with earlier studies, the number of newly synthesized polypeptides was increased by 30%. Over 300 species were separated by two-dimensional PAGE, and size classes up to 130,000 daltons were present, as compared to 70,000 in an earlier report. The polypeptides synthesized by human cerebral cortex and cerebellum were indistinguishable. However, several appeared to be uniquely human when compared with the products synthesized by mouse brain mRNA. The method described for the preparation of postmortem human brain mRNA eliminates the need to prepare polysomes, which are recovered in variable and low yield from the postmortem human brain. The procedure appears applicable to studies on the synthesis of moderately large human brain polypeptides and for investigations of brain protein polymorphism when relatively large numbers of products are required for analysis.

Proteolytic maturation of the turnip-yellow-mosaic-virus polyprotein coded in vitro occurs by internal catalysis

The genomic RNA of turnip yellow mosaic virus is translated in vitro into two major high-molecular-weight proteins, the larger of which (Mr 195 000) undergoes post-translational cleavage. The mechanism of formation of the primary cleavage products (Mr 120 000 and Mr 78 000) of the 195 000-Mr protein has been examined. The fact that cleavage partly occurs at a rate insensitive to dilution of the 195 000-Mr protein is suggestive of an intramolecular mechanism of proteolytic maturation.

Effect of secondary structure of messenger ribonucleic acid on the formation of initiation complexes with prokaryotic and eukaryotic ribosomes

The effect of modification of the secondary structure of phage f2 RNA and brome mosaic virus (BMV) RNA 3 on the formation of initiation complexes in Escherichia coli and wheat germ protein-synthesizing systems was studied. Modification of the RNAs was achieved by using O-methylhydroxylamine, which specifically reacts with cytosines; this leaves the initiation codons unchanged and, under denaturing conditions, leads to irreversible unfolding of the RNA. E. coli ribosomes interact with newly exposed AUG/GUG codons in the modified templates forming polysomes, whereas they form monosomes with native f2 RNA or BMV RNA 3. With wheat germ ribosomes, disomes are formed in the presence of BMV RNA 3, either native or modified. With f2 RNA, eukaryotic ribosomes form monosomes, independent of the secondary structure of the template. The results indicate that, in contrast to prokaryotic ribosomes, binding of eukaryotic ribosomes to f2 RNA or BMV RNA 3 is not affected by modification of the secondary structure of these messengers.

Preproceruloplasmin is a primary product of cell-free translation of ceruloplasmin messenger RNA

Biosynthesis of ceruloplasmin was studied in wheat germ extract programmed with polysomal RNA from rat liver. Optimal potassium concentration for the total protein-synthesizing activity and for the synthesis of immunoreactive ceruloplasmin was 96 and 186 mM respectively. 7-methylguanosine 5'-monophosphate caused two-fold inhibition of the cell-free synthesis of ceruloplasmin. Immunoprecipitated ceruloplasmin that was synthesized at optimal potassium concentration was a homogeneous polypeptide of a molecular weight about 84 kD. The addition of membrane fractions from rat liver to the incubation mixture caused the conversion of the 84 kD polypeptide into 80 kD and 65 kD polypeptides that are similar to proceruloplasmins synthesized in rat liver during in vivo pulse labelling. The suggestion is made that 84 kD polypeptide is a primary product of the translation of ceruloplasmin mRNA (preproceruloplasmin).

Highly purified ceruloplasmin messenger RNA from rat liver. Physico-chemical and functional characteristics

Highly purified ceruloplasmin mRNA was isolated from rat liver polyribosomes. The molecular weight of ceruloplasmin mRNA is in a range from 1.05 to 1.25 . 10(6) daltons which is large enough to code for a putative precursor of ceruloplasmin (approximately 700 amino acid acids). Ceruloplasmin mRNA contains 3'-terminal poly(A) the length of which varies from 38 to 165 nucleotides. The 5'-end of ceruloplasmin mRNA is blocked with confronting m7G residue which is a component of cap I (m7G5'ppp5'XmpAp). The addition of ceruloplasmin mRNA to wheat-germ cell free system programmed the synthesis of a product that was largely precipitated by anti-ceruloplasmin immunoglobulins. The translation product was homogeneous in polyacrylamide gel-sodium dodecylsulfate electrophoresis. Cell-free translation of ceruloplasmin mRNA was sensitive to inhibition by cap analogue.

The preparation of biologically active messenger RNA from human postmortem brain tissue

Messenger RNA (mRNA) was extracted from human postmortem brain tissue by alkaline phenol extraction of polysomes followed by oligo (dT)-cellulose chromatography. The mRNA preparations stimulated protein synthesis in a cell-free system containing wheat germ homogenate. The products of protein synthesis were analyzed by one- and two-dimensional gel electrophoresis. These analyses indicated that numerous polypeptides, including tubulin subunits and actin isomers, were synthesized by the human mRNA. The molecular weight range of polypeptides synthesized by human mRNA fractions from two brain specimens were identical, and analysis by two-dimensional gel electrophoresis indicated qualitatively similar products. The yield of mRNA extracted per gram of human tissue was less than the yield obtained with rat forebrains from animals sacrificed immediately before brain removal and mRNA purification. A decrease in the amount of polysomes isolated from human tissue relative to rat brain tissue was a major factor contributing to the low yield. The molecular weight distribution of polypeptides synthesized by human and rat brain mRNA fractions in wheat germ homogenate was similar; thus, there was no indication for selective breakdown or inactivation of high molecular weight mRNA species in the human tissue. Our studies indicate that it is possible to utilize postmortem tissue for molecular biological investigations of human brain mRNA.

Physical and functional mapping of rat-liver mitochondrial DNA

Rat-liver mitochondrial DNA (mtDNA) contains 2 cleavage sites of the restriction endonuclease Xbal. The molecular sizes of restriction fragments are 6.6 X 10(6) and 3.7 X 10(6) D. The results of partial cleavage of mtDNA with EcoRI allow the fragment F (0.32 X 10(6) D) to be localized in the sequence ABCEGFHDA. The functional map of mtDNA is constructed for two genes of the ATP-ase mRNAs from rat-liver mitochondria. Molecular hybridization shows that the ATPase genes are located in fragment B and in the GEHD area of mtDNA EcoRI cleavage.

Reversal of the inhibitory effects of the pokeweed antiviral protein upon protein synthesis

Protein synthesis directed by natural mRNA is more sensitive to the inhibitory action of the pokeweed antiviral protein than synthesis directed by poly-(uridylic acid). Investigations into the nature of this difference revealed that pokeweed antiviral protein does not inhibit the initiation stage of protein synthesis and that the expression of pokeweed antiviral protein inhibition is dependent upon the K+ and Mg2+ concentrations used in the protein synthesis assay. Ribosomes treated with pokeweed antiviral protein function as efficiently as untreated ribosomes if assayed at either high Mg2+ or low K+ concentrations. The influence of ionic conditions upon the individual elongation factor reactions shows that pokeweed antiviral protein inhibition of the elongation factor two translocation reaction is sensitive to ionic conditions but that the inhibition of the elongation factor one-mediated enzymatic binding is not sensitive to changes in these conditions. The results suggest that the unknown enzymatic effect of pokeweed antiviral protein produces a conformational change in ribosome, which is reversed under conditions which favor a more compact ribosomal structure.

Purification and characterisation of adenosine-3',5'-phosphate-independent protein kinase from wheat germ

cAMP-independent protein kinase was isolated from the wheat germ and purified to electrophoretic homogeneity. The molecular weight of enzyme was approximately 20,000, Km for ATP was (1 +/- 0.2) x 10(-5) M. V was 215 nmol phosphate mg enzyme-1 min-1, and the isoelectric point was at pH 9.2. The enzyme promotes phosphorylation of casein and crude wheat germ ribosomes.

Cell-free translation of exogenous mRNA in extracts from dry pea primary axes

Extracts from the primary axes of dry pea (Pisum sativum L.) seeds are able to perform an initiation-dependent translation of exogenous mRNA. SDS polyacrylamide gel electrophoresis of the products synthesized under direction of alfalfa mosaic virus RNA (AMV-RNA) and tobacco mosaic virus RNA (TMV-RNA) shows that the fidelity of translation in this pea system is at least as high as in a wheat embryo cell-free protein synthesizing system. The endogenous messengers are also efficiently translated in extracts from the primary axes of pea seeds. The direct translation of these messengers in a homologous cell-free system may be of interest for a study of the products coded for by the long-lived messengers present in this plant.