Characterization of a highly efficient protein synthesizing system derived from commercial wheat germ

Wheat germ systems for cell-free protein expression

Cell-free protein expression plays an important role in biochemical research. However, only recent developments led to new methods to rapidly synthesize preparative amounts of protein that make cell-free protein expression an attractive alternative to cell-based methods. In particular the wheat germ system provides the highest translation efficiency among eukaryotic cell-free protein expression approaches and has a very high success rate for the expression of soluble proteins of good quality. As an open in vitro method, the wheat germ system is a preferable choice for many applications in protein research including options for protein labeling and the expression of difficult-to-express proteins like membrane proteins and multiple protein complexes. Here I describe wheat germ cell-free protein expression systems and give examples how they have been used in genome-wide expression studies, preparation of labeled proteins for structural genomics and protein mass spectroscopy, automated protein synthesis, and screening of enzymatic activities. Future directions for the use of cell-free expression methods are discussed.

Translation of mRNAs for subunits of chloroplast coupling factor 1 in spinach

The chloroplast coupling factor 1 consists of five nonidentical subunits, three of which (alpha, beta, and epsilon subunits) have been shown in several laboratories to be synthesized within chloroplasts. The site of synthesis of the remaining two (gamma and delta subunits) was investigated by analyzing products directed by spinach leaf RNAs in wheat germ and reticulocyte translation systems in vitro. It was found that poly(A)(+) RNA directs the synthesis of two distinct polypeptides, one of which is immunochemically related to the gamma subunit but is 4,000 daltons larger. The other shares antigenic sites with the delta subunit but is 8,000 daltons larger. When wheat germ or reticulocyte translation systems were programmed with RNAs from purified chloroplasts, the only products related to CF(1) that we could detect were a putative precursor of beta, 2,000 daltons larger than the mature subunit, and some smaller polypeptides, which appear to be incomplete translation products of beta. From these results it appears likely that the gamma and delta subunits are synthesized in the cytoplasm as larger precursors and that beta is synthesized within the chloroplast as a precursor.

Correlation between particle multiplicity and location on virion RNA of the assembly initiation site for viruses of the tobacco mosaic virus group

The initiation site for reconstitution on genome RNA was determined by electron microscopic serology for a watermelon strain of cucumber green mottle mosaic virus (CGMMV-W), which is chemically and serologically related to tobacco mosaic virus (TMV). The initiation site was located at the same position as that of the cowpea strain, a virus that produces short rods of encapsidated subgenomic messenger RNA for the coat protein (a two-component TMV), being about 320 nucleotides away from the 3' terminus, and hence within the coat protein cistron. Although CGMMV-W was until now believed to be a single-component TMV, the location of the initiation site indicated the presence of short rods containing coat protein messenger RNA in CGMMV-W-infected tissue, as in the case for the cowpea strain. We found such short rods in CGMMV-W-infected tissue. The results confirmed our previous hypothesis that the site of the initiation region for reconstitution determines the rod multiplicity of TMV. The finding of the second two-component TMV, CGMMV, indicates that the cowpea strain of TMV is not unique in being a two-component virus and that the location of the assembly initiation site on the genome RNA can be a criterion for grouping of viruses.

Cloning and structure determination of cDNA for cutinase, an enzyme involved in fungal penetration of plants

The primary structure of cutinase, an extracellular fungal enzyme involved in the penetration of plants by pathogenic fungi, has been determined from the nucleotide sequence of cloned cDNA. Clones containing cDNA made from poly(A)(+) RNA isolated from fungal cultures induced to synthesize cutinase were screened for their ability to hybridize with the [(32)P]cDNA for mRNA unique to the induced culture. The 75 cDNA clones thus identified were screened for the cutinase genetic code by hybrid-selected translation and examination of products with anti-cutinase IgG. This method yielded 15 clones containing cDNA for cutinase, and Southern blots showed that the size of the cDNA inserts ranged from 279 to 950 nucleotides. Blot analysis showed that cutinase mRNA contained 1050 nucleotides, indicating that the clone containing 950 nucleotides represented nearly the entire mRNA. This near-full-length cDNA and the restriction fragments subcloned from it were sequenced by a combination of the Maxam-Gilbert and the phage M13-dideoxy techniques. cDNAs from two other clones, containing the bulk of the coding region for cutinase, were also completely sequenced, and the results confirmed the sequence obtained with the first clone. A peptide isolated from a trypsin digest of cutinase was sequenced and the amino acid sequence as well as the initiation and termination codons were used to identify the coding region of the cDNA. The primary structure of the enzyme so far determined by amino acid sequencing ( approximately 40% of the total) agreed completely with the nucleotide sequencing results. Thus, the complete primary structure of the mature enzyme and that of the signal peptide region were ascertained.

Synthesis and processing of maize storage proteins in Xenopus laevis oocytes

Xenopus oocytes injected with zein mRNAs efficiently synthesized maize storage proteins for prolonged periods. Under optimal conditions, zein was synthesized at 3 ng/hr and represented approximately 10% of the total protein synthesized in the oocyte. The mRNA from the normal maize inbred line directed synthesis of all the major zein components; however, products of mRNA from the opaque-2 mutant did not contain the largest zein component. Zein proteins synthesized in the oocyte were 2000 daltons smaller than proteins synthesized by cell-free translation of mRNAs in the wheat germ and reticulocyte systems. This result, which suggested that the oocyte processed prezein polypeptides into native zein proteins, was confirmed by amino-terminal sequence analysis of zein proteins from the oocytes. Cyanogen bromide cleavage of translation products from oocytes and the wheat germ system confirmed the existence of several proteins within each of the major zein components. However, we were unable to detect the presence of signal sequences on zein peptides by this technique.

In vitro translation of plant viral RNA

This unit describes the preparation of a wheat germ extract that provides all the soluble components of the plant translational machinery. Many RNA plant viruses have positive-strand genomes and the viral RNA serves as messenger RNA (mRNA). The preparation of mRNA by in vitro transcription is also described. The translation assay requires optimization of the amount of wheat germ extract, level of mRNA, and the concentration of Mg(2+) and K(+) for each mRNA. The translational efficiency of RNAs or mutants may be compared (e.g., capped versus uncapped RNAs to measure cap-independent translation) or the amount/size of the protein product may be determined.

Artifacts are responsible for the translational activity of polyribosome preparations isolated from alfalfa mosaic virus-infected tobacco leaves

We observed that polyribosome preparations isolated from alfalfa mosaic virus (A1MV)-infected tobacco leaves were contaminated with virion-derived material which could not be removed completely by sucrose gradient centrifugation or by magnesium ion precipitation. Upon incubation of polyribosome preparations with S 100 extracts from reticulocyte lysates, viral-encoded proteins were produced. Aurintricarboxylic acid (ATA), an inhibitor of initiation of translation, was used to inhibit de novo translation of the RNAS contaminating the polyribosome preparations. ATA concentrations, which did not inhibit peptide chain elongation on in vitro-produced polyribosomes, completely inhibited the translational activity of the tobacco polyribosomes. Hence the protein synthetic capacity of the tobacco polyribosome preparations is due to de novo translation of virion-derived material by vacant ribosomes present in the complementing S 100 extract. Efforts to activate the tobacco polyribosomes remain unsuccessful.

Identification of potyviral amorphous inclusion protein as a nonstructural, virus-specific protein related to helper component

Antisera to amorphous inclusion (AI) proteins associated with infections by pepper mottle virus (PeMV) and the watermelon mosaic virus-1 strain of papaya ringspot virus (PRSV-W) were used to probe in vitro translation products of the viral RNAs. The major translation product of PeMV RNA in the rabbit reticulocyte lysate (RRL) system was a previously reported polypeptide of apparent molecular weight 78,000 (Mr 78K). It reacted with anti-AI serum, whereas the major translation product in the wheat germ (WG) system was a 30K polypeptide that did not react with the antiserum. These results, the Mr values, and analyses of peptides generated by partial digestion with proteinase indicate that the amino acid sequences of the 30K polypeptide and the (Mr) 51K AI protein are distinct subsets of the 78K polypeptide amino acid sequence. Similar results were obtained with PRSV-W except that the Mr values of the corresponding translation products are 110K (RRL) and 60K (WG). Thus the 5'-most region of the PeMV and PRSV-W RNAs (corresponding to 78K and 110K, respectively) appears to encode two proteins rather than one as previously supposed on the basis of RRL translation products. Reciprocal serological tests revealed that the tobacco vein mottling virus aphid transmission helper component protein was related to AI protein. There is direct evidence that the AI represent another potyviral-coded nonstructural protein and the first evidence that a biologically functional protein is related to a component of a potyviral inclusion.

Identification of the 30K protein of TMV by immunoprecipitation with antibodies directed against a synthetic peptide

A synthetic hexadecapeptide corresponding to the predicted C-terminal sequence of the 30K protein of TMV has been coupled to bovine serum albumin and used to raise antibodies in rabbits. The resulting antiserum reacted with the 30K protein translated in vitro. We report the use of this antiserum in the first detection of the 30K protein in vivo, in TMV-infected tobacco protoplasts. Several proteins, the so called family of 30K-related peptides, were immunoprecipitated among in vitro translation products, but only the 30K protein was immunoprecipitated from TMV-infected protoplasts.

Lucerne transient streak virus RNA and its translation in rabbit reticulocyte lysate and wheat germ extract

Two abundant, encapsidated RNAs of lucerne transient streak virus (LTSV) are the 1.5 x 10(6) molecular weight (Mr) linear RNA-1 and both circular (RNA-2) and linear (RNA-3) forms of a 0.15 x 10(6) Mr viroid-like RNA. Two additional discrete minor RNAs, Mr 0.35 x 10(6) and 0.07 x 10(6), and a heterogeneous mixture of RNAs in the Mr range 0.05 to 1.0 x 10(6) are reported. Principal polypeptides translated from unfractionated LTSV RNA in rabbit reticulocyte lysate were of Mr 105,000 (p105), 78,000 (p78), and 33,000 (p33), the last not easily detected after translation in wheat germ extracts. All apparently are encoded in RNA-1. However, p33, which was precipitated by antibody of LTSV particles and presumably is the major capsid protein, was more readily translated from a smaller, most likely the Mr 0.35 x 10(6), RNA. Partial proteolysis and other tests indicate that p105 has a carboxyl terminal extension of p78 amino acid sequences and that neither shares sequences with p33. No translation products were attributed to RNA-2, RNA-3 or the Mr 0.07 x 10(6) RNA.

Expression and purification of recombinant wheat translation initiation factors eIF1, eIF1A, eIF4A, eIF4B, eIF4F, eIF(iso)4F, and eIF5

Protein synthesis initiation factors from wheat germ were cloned into E. coli expression vectors for expression and purification. The ability to obtain large amounts of functional initiation factors and mutants of the factors will facilitate the biophysical and biochemical analysis of the process of initiation in plants. The initiation factors, eIF1, eIF1A, eIF4A, eIF4B, eIF4F, eIF(iso)4F, and eIF5, were successfully expressed and purified from E. coli. In most cases, the use of 6X-histidine tags was avoided to prevent any possible artifacts of folding or activity because of the presence of the tag. The amounts of highly purified wheat initiation factors obtained ranged from 0.5 to 24mg of protein per liter of culture, depending on the particular initiation factor. The initiation factors were of very high purity, and the activities of the wheat recombinant factors purified from E. coli were found to be comparable to or better than those purified from wheat germ.

Translation of Zea mays endosperm sucrose-synthase mRNA in vitro

mRNA of 23-day-old maize endosperm was translated both in wheat germ extracts and rabbit reticulocyte lysates. A protein with an apparent molecular weight of 88,000 comigrates in dodecylsulfate/polyacrylamide electrophoresis with sucrose synthase. This protein is precipitated with an antiserum against sucrose synthase and shows the same protease digestion pattern as the enzyme. It is not synthesized with mRNA extracted from sh/sh mutant kernels lacking sucrose synthase. By these criteria, the protein is the translation product in vitro of sucrose synthase mRNA. The separation of mRNA in methylmercury-hydroxide--agarose gels and subsequent translation indicates a length of sucrose synthase mRNA of 2800 nucleotides which is compatible with the coding length necessary for a protein with a molecular weight of 88,000 plus untranslated sequences.

Translation and phosphorylation of wheat germ lysate: phosphorylation of wheat germ initiation factor 2 by casein kinase II and in N-ethylmaleimide-treated lysates

Previously, we observed that N-ethylmaleimide (NEM), a thiol-alkylating agent, was found to stimulate the phosphorylation of several proteins in translating wheat germ (WG) lysates, including the phosphorylation of alpha, the p41-42 doublet subunit, and beta, the p36 subunit, of the WG initiation factor 2 (eIF2). We find now that NEM increases phosphorylation of several proteins significantly in lysates which are moderate or low in their translation compared to optimally active lysates. Heat treatment, which stimulates oxidation of protein sulfhydryls, decreases the translation and phosphorylation ability of WG lysates. The decrease in phosphorylation, but not translation, that occurs in heat-treated lysates is prevented very efficiently by NEM and partially by reducing agents such as dithiothreitol (DTT) and GSH. DTT prevents, however, completely the loss of sulfhydryl content of heat-treated WG lysates and does not at all prevent heat-induced inhibition of translation. In contrast, DTT prevents completely the diamide-induced translational inhibition and also the loss of sulfhydryl content. These findings therefore suggest that in addition to the maintenance of sulfhydryl groups, heat-labile proteins and their interactions with other proteins play an important role in overall translation and phosphorylation. It is also observed here that heat treatment stimulates the phosphorylation of rabbit reticulocyte eIF2 alpha but not the alpha subunit (p41-42 doublet) of WG eIF2. A phosphospecific anti-eIF2 alpha antibody recognizes the WG eIF2 alpha(P) that is phosphorylated by an authentic eIF2 alpha kinase such as double-stranded RNA-dependent protein kinase, but it is unable to recognize the eIF2 alpha that is phosphorylated in NEM-treated lysates. These findings therefore suggest that phosphorylation of WG eIF2 alpha in NEM-treated lysates occurs on a site different from the serine 51 residue that is phosphorylated by authentic eIF2 alpha kinases. In addition, it also suggests that WG eIF2 alpha, unlike reticulocyte eIF2 alpha, is phosphorylated by eIF2 alpha kinases and also by other kinases. Consistent with this idea, it has been observed here that casein kinase II (CKII) phosphorylates WG eIF2 alpha and the phosphorylation is enhanced by NEM in vitro and in lysates. The phosphopeptide analysis suggests that WG eIF2 alpha has separate phosphorylation sites for CKII and heme-regulated eIF2 alpha kinase (a well-characterized mammalian eIF2 alpha kinase), and NEM-induced phosphorylation in WG lysates resembles CKII-mediated phosphorylation.

Stimulation of translation by reactive oxygen species in a cell-free system

Wheat germ lysate was used as a model system for in vitro translation. We show that an increase of the exchange surface between the reaction mixture and the atmosphere enhanced the amount of incorporated cysteine, indicating that early arrest of protein synthesis previously observed in such a system was due to oxygen starvation in the reaction mixture. This hypothesis was confirmed since the amount of proteins synthesized and the rate of translation increased when oxygen was added. We show that an addition of hydrogen peroxide to the translation mixture had the same effect as oxygen, allowing us to postulate that stimulation could be due to a common property between both molecules: the oxidizing behaviour. Free radicals in in vitro translation were believed to be involved since the utilization of iron chelating agents inhibited translation. This hypothesis was emphasized by the positive effect of a free radical generating system and the negative effect of free radical scavengers. These experiments suggest that the superoxide radical plays an important role in in vitro translation.

Characterization of a novel nodulin gene in soybean that shares sequence similarity to the gene for nodulin-24

A gene encoding for nodulin-16 (N-16) was isolated from a soybean genomic library. Nucleotide sequence analysis of the cDNA and the genomic clone of N-16 indicated that the coding region of this gene is 330 bp long and is interrupted by a single intron of 494 bp. The coding region of the N-16 gene shows a high degree of localized sequence similarity with the coding sequence of soybean nodulin-24 (N-24). Sequence similarity between the two genes is limited to the coding region of 90 bp in the first exon and the first 54 bp in the second exon of the N-16 gene which is repeated as the 2nd, 3rd, and 4th exons in the N-24 gene. The N-24 gene has been postulated to be a result of repeated duplication of an insertion element consisting of the 54 bp exon and the flanking intron sequences. In the absence of sequence similarity in the regions flanking the 54 bp sequence between the N-16 and N-24 genes, the N-16 gene does not appear to be the ancestral gene. Both N-16 and N-24 have a similar hydrophobic amino terminal end suggesting that N-16 like N-24 is targeted to the peribacteroid membrane. Southern analysis of soybean genomic DNA shows the presence of other related sequences to the N-16 gene, one of which is found to be closely linked to it. Analysis of the temporal accumulation of the N-16 transcripts during nodule development in effective and ineffective nodules suggests that N-16 and related genes might differ from leghemoglobin and some other late nodulin genes in their mechanism of regulation.

Glutathione S-transferase in yeast: induction of mRNA, cDNA cloning and expression in Escherichia coli

Glutathione S-transferase Y-2 mRNA synthesis was induced in yeast Issatchenkia orientalis approximately 37-fold by cultivation with o-dinitrobenzene. A cDNA library complementary to poly (A)+RNA of I. orientalis grown with o-dinitrobenzene was screened by colony hybridization. Twenty positive clones were obtained from 6,000 clones and seven of twenty positive clones expressed glutathione S-transferase activity in E. coli. One of the expressing clones harboring plasmid pHT108 had 28 times more glutathione S-transferase activity induced by Isopropyl-beta-D-thio-galactopyranoside than a strain harboring plasmid pUC118. Expressed glutathione S-transferase Y-2 protein comigrated with yeast glutathione S-transferase Y-2 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as detected by immunoblot analysis.

Three distinct ribonucleoproteins from tobacco chloroplasts: each contains a unique amino terminal acidic domain and two ribonucleoprotein consensus motifs

Chloroplasts contain their own genetic system. Eighteen different split genes have been found among approximately 130 chloroplast genes from higher plants. However, little is known about the chloroplast splicing system. Mammalian heterogeneous nuclear ribonucleoproteins (hnRNP proteins) have been shown to be involved in splicing. We applied a purification procedure developed for HeLa cell hnRNP proteins, which uses a single-stranded DNA (ssDNA) affinity column, directly to the tobacco chloroplast lysate to isolate their chloroplast counterparts. Four proteins (mol. wt approximately 30 kd) bound strongly to the column. The amino-terminal sequences of three of them were determined and their cDNA clones were isolated from a tobacco leaf cDNA library. Sequence analysis of these clones revealed that all three proteins contain two ribonucleoprotein consensus sequences (RNP-CS), confirming their ribonucleoprotein (RNP) nature. The presence of putative transit peptides in their predicted protein sequences, and an in vitro import experiment confirmed they are located in the chloroplast. This is the first report of organellar proteins containing RNP-CS. In addition, these three chloroplast proteins have a very acidic amino-terminal domain, a novel feature among RNP proteins identified so far. They are expressed both in leaves and roots; their mRNA levels showed different light modulation in mature leaves. The three proteins might be involved in splicing and/or processing of chloroplast RNAs.

Molecular cloning and nucleotide sequence of full-length cDNA for ascorbate oxidase from cultured pumpkin cells

A lambda gt11 cDNA expression library was constructed from size-fractionated poly(A)-rich RNA of cultured pumpkin cells. A full-length cDNA clone for ascorbate oxidase mRNA was selected from the library by screening with synthetic oligonucleotides designed from the amino-terminal sequence of ascorbate oxidase protein. The identity of the clone was confirmed by comparing the amino acid sequence deduced by nucleotide sequence analysis with that determined for the amino-terminal sequence of pumpkin ascorbate oxidase. The nucleotide sequence of the cDNA insert was found to contain an open reading frame of 579 codons corresponding to a signal peptide of 30 amino acids and the mature 549-residue ascorbate oxidase. Furthermore, it was found that the amino acid sequence deduced from the nucleotide sequence of the cDNA insert contained four potential N-glycosylation sites and copper-binding amino acid residues located in four regions where the sequence was identical or nearly identical to those of the other known blue multicopper oxidases Neurospora crassa laccase and human ceruloplasmin.

Context effects and inefficient initiation at non-AUG codons in eucaryotic cell-free translation systems

The context requirements for recognition of an initiator codon were evaluated in vitro by monitoring the relative use of two AUG codons that were strategically positioned to produce long (pre-chloramphenicol acetyl transferase [CAT]) and short versions of CAT protein. The yield of pre-CAT initiated from the 5'-proximal AUG codon increased, and synthesis of CAT from the second AUG codon decreased, as sequences flanking the first AUG codon increasingly resembled the eucaryotic consensus sequence. Thus, under prescribed conditions, the fidelity of initiation in extracts from animal as well as plant cells closely mimics what has been observed in vivo. Unexpectedly, recognition of an AUG codon in a suboptimal context was higher when the adjacent downstream sequence was capable of assuming a hairpin structure than when the downstream region was unstructured. This finding adds a new, positive dimension to regulation by mRNA secondary structure, which has been recognized previously as a negative regulator of initiation. Translation of pre-CAT from an AUG codon in a weak context was not preferentially inhibited under conditions of mRNA competition. That result is consistent with the scanning model, which predicts that recognition of the AUG codon is a late event that occurs after the competition-sensitive binding of a 40S ribosome-factor complex to the 5' end of mRNA. Initiation at non-AUG codons was evaluated in vitro and in vivo by introducing appropriate mutations in the CAT and preproinsulin genes. GUG was the most efficient of the six alternative initiator codons tested, but GUG in the optimal context for initiation functioned only 3 to 5% as efficiently as AUG. Initiation at non-AUG codons was artifactually enhanced in vitro at supraoptimal concentrations of magnesium.

Context effects and inefficient initiation at non-AUG codons in eucaryotic cell-free translation systems

The context requirements for recognition of an initiator codon were evaluated in vitro by monitoring the relative use of two AUG codons that were strategically positioned to produce long (pre-chloramphenicol acetyl transferase [CAT]) and short versions of CAT protein. The yield of pre-CAT initiated from the 5'-proximal AUG codon increased, and synthesis of CAT from the second AUG codon decreased, as sequences flanking the first AUG codon increasingly resembled the eucaryotic consensus sequence. Thus, under prescribed conditions, the fidelity of initiation in extracts from animal as well as plant cells closely mimics what has been observed in vivo. Unexpectedly, recognition of an AUG codon in a suboptimal context was higher when the adjacent downstream sequence was capable of assuming a hairpin structure than when the downstream region was unstructured. This finding adds a new, positive dimension to regulation by mRNA secondary structure, which has been recognized previously as a negative regulator of initiation. Translation of pre-CAT from an AUG codon in a weak context was not preferentially inhibited under conditions of mRNA competition. That result is consistent with the scanning model, which predicts that recognition of the AUG codon is a late event that occurs after the competition-sensitive binding of a 40S ribosome-factor complex to the 5' end of mRNA. Initiation at non-AUG codons was evaluated in vitro and in vivo by introducing appropriate mutations in the CAT and preproinsulin genes. GUG was the most efficient of the six alternative initiator codons tested, but GUG in the optimal context for initiation functioned only 3 to 5% as efficiently as AUG. Initiation at non-AUG codons was artifactually enhanced in vitro at supraoptimal concentrations of magnesium.

Phase-Specific Polypeptides and Poly(A) RNAs during the Cell Cycle in Synchronous Cultures of Catharanthus roseus Cells

This study shows an overall analysis of gene expression during the cell cycle in synchronous suspension cultures of Catharanthus roseus cells. First, the cellular cytoplasmic proteins were fractionated by two-dimensional gel electrophoresis and visualized by staining with silver. Seventeen polypeptides showed qualitative or quantitative changes during the cell cycle. Second, the rates of synthesis of cytoplasmic proteins were also investigated by autoradiography by labeling cells with [(35)S]methionine at each phase of the cell cycle. The rates of synthesis of 13 polypeptides were found to vary during the cell cycle. The silverstained electrophoretic pattern of proteins in the G(2) phase in particular showed characteristic changes in levels of polypeptides, while the rates of synthesis of polypeptides synthesized during the G(2) phase did not show such phase-specific changes. This result suggests that posttranslational processing of polypeptides occurs during or prior to the G(2) phase. In the G(1) and S phases and during cytokinesis, several other polypeptides were specifically synthesized. Finally, the variation of mRNAs was analyzed from the autoradiograms of in vitro translation products of poly(A)(+) RNA isolated at each phase. Three poly(A)(+) RNAs increased in amount from the G(1) to the S phase and one poly (A)(+) RNA increased preferentially from the G(2) phase to cytokinesis.

Characterization of the kafirin gene family from sorghum reveals extensive homology with zein from maize

Electrophoretic analysis of translation products of polyadenylated RNA isolated from mid-maturation sorghum seed in the presence of [(35)S]met, [(3)H]leu, or [(3)H]val revealed two major proteins of kDa and 21 kDa. These products were not detected when [(3)H]lys was supplied as the radioactive substrate. Under similar electrophoretic conditions, kafirin (a major seed storage prolamin of sorghum), migrated as two bands of 22 kDa and 19 kDa. Sequence analysis of two cDNA clones (pSK8 and pSKR2) from sorghum seed mRNA revealed them to be highly homologous with each other and to the 22 kDa zeins from maize, suggesting that they represented kafirin cDNAs. Compared with pSKR2, pSK8 had an insertion of 24 nucleotides and a deletion of 24 nucleotides, so that the coding regions were nearly identical in length. The deduced amino acid sequence for these cDNA clones reveals that kafirin, like zein, is rich in glutamine and nonpolar amino acids, but contains no lysine. Both kafirin and zein have a 21 amino acid signal peptide exhibiting 80% homology and eight copies of a repetitive amino acid block in the C-terminal domain with the consensus: infI (supP) LL finP (supA) LN infQ (supP) LALANPAAYLQQQQ.The kafirin cDNAs were used as probes to screen a sorghum genomic library; one genomic clone (λGK.1) was sequenced and found to be very similar (97.8%) to the pSK8 cDNA clone. Clone λGK.1 contains features typical for a functional gene in that the intronless open reading frame encoding 268 amino acids is flanked at the 5' end by sequences corresponding to the CAAT and TATA promoter boxes (positioned at about -60 and -30 bp, respectively, from the transcriptional initiation site), and at the 3' end by a consensus polyadenylation signal. In common with zein genomic clones, kafirin clones contain a 15 basepair consensus sequence centered at postion -320 relative to the transcriptional initiation site. Under similar hybridization conditions, genomic reconstruction analysis using an oligonucleotide probe indicated the presence of less than 20 copies of kafirin per haploid sorghum genome compared with approximatley 140 copies of zein per haploid maize genome.

Stability of protein and mRNA in human postmortem liver--analysis by two-dimensional gel electrophoresis

The method of two-dimensional polyacrylamide gel electrophoresis has been used to investigate the post mortem stability of protein and mRNA in human liver. The electrophoretic mobility of proteins and of the in vitro translation products of the mRNA were found to be essentially unaffected by incubation of the liver at 37 degrees C for up to 2 h or at 4 degrees C for up to 16 h. This study indicates that the major protein and mRNA species in liver are stable enough following death to allow meaningful studies on tissue collected under standard autopsy conditions.

Cell-free translation of human lysosomal alpha-glucosidase: evidence for reduced precursor synthesis in an adult patient with glycogenosis type II

Early events in the biosynthesis of alpha-glucosidase (EC 3.2.1.20) were studied in a wheat-germ cell-free translation system, using control and mutant RNA. In vitro, the primary translation product of the alpha-glucosidase mRNA is a 100 kDa protein. When canine microsomal membranes are added to the translation system, the nascent alpha-glucosidase precursor is cotranslationally transported across the microsomal membranes, yielding a 110 kDa glycosylated form. This protein has the same electrophoretic characteristics as the alpha-glucosidase precursor observed after in vivo labeling of control fibroblasts. Inhibition of glycosylation in vivo by tunicamycin or deglycosylation of the in vivo synthesized alpha-glucosidase precursor by glycopeptidase F reveals a core protein similar in molecular mass to the primary translation product. Total RNA from a patient with the adult form of glycogenosis type II is not able to direct the synthesis of normal amounts of alpha-glucosidase in vitro. Northern blot analysis of the RNA, using cloned alpha-glucosidase cDNA sequences as a probe, demonstrates that in this patient the amount of the 3.4 kb alpha-glucosidase mRNA is highly reduced. The results indicate that the synthesis or stability of the mRNA is affected.

The 3' untranslated region of the human interferon-beta mRNA has an inhibitory effect on translation

In vitro-transcribed human interferon-beta (IFN-beta) mRNA, which contains all the sequence of the natural molecule, is poorly translated in a reticulocyte lysate or when injected in Xenopus oocytes. This low level of translation is due to an inhibition by the 5' and 3' untranslated regions (UTRs). Indeed, the replacement of these sequences by those of Xenopus beta-globin mRNA dramatically increases the translational efficiency of the mRNA, especially in oocytes. This phenomenon is not due to a difference in mRNA stability since both native and chimeric mRNAs remain undegraded, at least during the translation period considered. Construction of different chimeric molecules having various combinations of 5' and 3' UTRs from IFN-beta or Xenopus beta-globin mRNA or a small sequence of SP6 polylinker as 5' UTR has revealed that the 3' UTR of IFN-beta in itself has a pronounced inhibitory effect on translation in the two translation systems from animal cells. Indeed, the addition of this 3' UTR at the 3' end of the coding region of a chicken lysozyme mRNA also causes a large decrease of its translational capacity in both systems. However, the nature of the 5' noncoding sequence influences the degree of translation inhibition exerted by the 3' UTR. Remarkably, we observed no difference in translation level when the different mRNAs were tested in a wheat germ extract.

Rat androgen-binding protein: evidence for identical subunits and amino acid sequence homology with human sex hormone-binding globulin

The cDNA for rat androgen-binding protein (ABP) was previously isolated from a bacteriophage lambda gt11 rat testis cDNA library and its identity was confirmed by epitope selection. Hybrid-arrested translation studies have now demonstrated the identity of the isolates. The nucleotide sequence of a near full-length cDNA encodes a 403-amino acid precursor (Mr = 44,539), which agrees in size with the cell-free translation product (Mr = 45,000) of ABP mRNA. Putative sites of N-glycosylation and signal peptide cleavage were identified. Comparison of the predicted amino acid sequence of rat ABP with the amino-terminal amino acid sequence of human sex hormone-binding globulin revealed that 17 of 25 residues are identical. On the basis of the predicted amino acid sequence the molecular weight of the primary translation product, lacking the signal peptide, was 41,183. Hybridization analyses indicated that the two subunits of ABP are coded for by a single gene and a single mRNA species. Our results suggest that ABP consists of two subunits with identical primary sequences and that differences in post-translational processing result in the production of 47,000 and 41,000 molecular weight monomers.

A simple gene-expression system for the small subunit of ribulose bisphosphate carboxylase in leaves ofNicotiana sylvestris

InNicotiana sylvestris only four transcripts coding for the small subunit of RUBISCO are present in leaves. They are very closely related as they are identical in the nucleotide sequence of the non-coding regions and show only three silent point differences in the region coding for the mature peptide.The main difference among these four transcripts lies in the length of the non-coding regions. Half of the SmRNA population as confirmed by direct RNA sequencing has an additional nucleotide sequence in the leader region. Two cDNAs have an additional nucleotide sequence at the end of the 3' non-coding region. Based on these criteria the transcripts were classified into two groups:.group I has a 73-nucleotide-long leader sequence and the nucleotides T, A and C at position 327, 432 and 519 in the coding region..group II has a 60-nucleotide-long leader sequence and the nucleotides C, G and T at these positions in the coding region.The two cDNAs showing a difference in the length of the 3' non-coding region belong to group II.The study of all these transcripts argues for the possibility that only two families of genes are expressed in leaves ofN. sylvestris.

A study of the role of metallothionein in the inherited copper toxicosis of dogs

The role of metallothionein (MT) was assessed in the copper-loading disease prevalent in Bedlington terriers. Fractionation of tissue supernatants over Sephadex G-75 showed that most of the additional cytosolic copper present in liver tissue of these dogs was bound to MT, and that substantially more MT-bound copper could be solubilized by detergent plus mercaptoethanol. Zinc contents were only slightly raised, although most of the extra zinc was associated with a 4000-Mr ligand. Ion-exchange chromatography revealed two isoproteins, MT1 and MT2, in all the dog liver samples examined. In Bedlington terrier liver, copper associated with both isoproteins was increased, although the increase for MT2 was greater than for MT1. The content of MT protein was also raised, although cell-free translations and RNA blots of total liver RNA showed that this increase was not associated with a rise in MT mRNA. The significance of these results to the mechanism of copper accumulation in the Bedlington terrier disorder is discussed.

Expression of nodule-specific glutamine synthetase genes during nodule development in soybeans

A cDNA clone (pcPvNGS-01) to glutamine synthetase (GS) mRNA from root nodules of Phaseolus vulgaris showed cross-hybridization to GS and mRNA from soybean root nodules, thus allowing its use as a probe to study the expression of GS genes during root nodule development in soybeans. Hybrid-select translation of root and nodule RNA of soybean with DNA from pcPvNGS-01, followed by 2D gel electrophoresis, showed six peptides in the root and an additional four peptides in the nodule which represent nodule-specific glutamine synthetase (GSn) gene products. The GSn gene products appeared for the first time between day 11 and 12 after infection, either concomitant with the onset of nitrogenase activity or immediately following it. The levels of expression of the GSn and leghemoglobin genes were not affected in young Fix(-) nodules formed by Bradyrhizobium japonicum strains that are defective in nitrogenase activity, suggesting that the induction of these two sets of host genes take place independent of nitrogenase activity. However, in Fix(-) nodules that are incapable of maintaining the peribacteroid membrane, GSn gene products were not detected while 1ba, 1bc2 and 1bc3 appeared. In both the timing of appearance during root nodule development and the effect of different bacterial mutations on the expression, GSn genes differ from most other nodulin genes examined (30), suggesting different regulatory mechanisms.

In vitro synthesis and assembly of photosystem II proteins of spinach chloroplasts

The synthesis and assembly of photosystem II (PS II) proteins of spinach chloroplasts were investigated in three different in vitro systems, i.e., protein synthesis in isolated chloroplasts (in organello translation), read-out translation of thylakoid-bound ribosomes, and transport of translation products from spinach leaf polyadenylated RNA into isolated chloroplasts. Polyacrylamide gel electrophoresis of labeled thylakoid polypeptides in the presence of sodium dodecyl sulfate revealed that the first two systems were capable of synthesizing the reaction center proteins of PS II (47 and 43 kDa), the herbicide-binding protein, and cytochrome b559. The reaction center proteins synthesized in organello were shown to bind chlorophyll and to assemble properly into the PS II core complex. One of the reaction center proteins translated by the thylakoid-bound ribosomes (47 kDa) was also found to be integrated in situ into the complex but was lacking bound chlorophyll. Incorporation of radioactivity into the three extrinsic proteins of the oxygen-evolution system (33, 24, and 18 kDa) was detected only when intact chloroplasts were incubated with the translation products from polyadenylated RNA, showing that these proteins are coded for by nuclear DNA. The occurrence of a precursor polypeptide 6 kDa larger than the 33-kDa protein was immunochemically detected in the translation products.

Translation of homologous and heterologous messenger RNAs in a yeast cell-free system

A stable mRNA-dependent cell-free translation system from Saccharomyces cerevisiae, prepared by a modification of the method of Hofbauer et al. [Eur. J. Biochem. 122 (1982) 199-203] was active in translation of exogenous homologous and heterologous mRNAs. Optimal translational activity required the addition of polyamines and yeast tRNA. The m transcript of the M segment of double-stranded RNA, synthesized in vitro using the killer virus-associated RNA polymerase, directed the synthesis of preprotoxin polypeptide (M-p32), which was immunologically identified using antitoxin antibody. Sindbis virus capsid protein and rabbit globin were also translated from their mRNAs. Translation was inhibited by puromycin, sparsomycin and anisomycin. Analogues of the 5'-terminal caps present on most eukaryotic mRNA molecules inhibited translation of added mRNAs, including capped mRNAs and the uncapped killer virus mRNA.

Molecular adaptations in catecholamine biosynthesis induced by cold stress and sympathectomy

Chronic cold stress and chemical sympathectomy are known to increase the synthesis and release of catecholamines in the adrenal medulla. Chromaffin cells adapt to altered functional requirements by increasing the synthesis of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. In this study, we investigated the molecular genetic mechanisms underlying these changes in enzyme activity. Estimates of TH mRNA levels were obtained by RNA dot-blot analysis with a cloned TH cDNA hybridization probe. Exposure to cold produced a 4.3-fold increase in the relative abundance of adrenomedullary TH mRNA. Increases in TH mRNA levels (90%) also were observed in the brainstem of cold-stressed animals. The relative amount of TH synthesized in vitro in a rabbit reticulocyte cell-free system, programmed with adrenal poly(A)+RNA, increased 4.3 times in cold-stressed rats. Alteration in TH mRNA abundance appears to be specific, as we observed no significant difference in the levels of total RNA or poly(A)+RNA in this tissue. In addition, the relative abundance of adrenomedullary TH mRNA increased by 60% 4 days after systemic administration of the neurotoxin 6-hydroxydopamine. This increase was transient and disappeared 2 weeks after the lesion. Changes in TH mRNA levels after cold stress or sympathectomy were eliminated by denervation of the adrenal gland. These results indicate that alterations in the relative abundance of TH mRNA mediate changes in TH activity induced by chronic stress or sympathectomy, and that these changes require an intact sympathetic input.

Biosynthesis of alpha-Amylase in Vigna mungo Cotyledon

In vitro translation of RNA extracted from Vigna mungo cotyledons showed that alpha-amylase is synthesized as a polypeptide with a molecular mass of 45,000, while cotyledons contain a form of alpha-amylase with a molecular mass of 43,000. To find out whether the 45,000 molecular mass polypeptide is a precursor to the 43,000 found in vivo, the cell free translation systems were supplemented with canine microsomal membrane; when mRNA was translated in the wheat germ system supplemented with canine microsomes, the 45,000 molecular mass form was not processed to a smaller form but the precursor form was partly processed in the membrane-supplemented reticulocyte lysate system. When V. mungo RNA was translated in Xenopus oocyte system, only the smaller form (molecular mass 43,000) was detected. Involvement of contranslational glycosylation in the maturating process of the alpha-amylase was ruled out because there was no effect of tunicamycin, and the polypeptide was resistant to endo-beta-H or endo-beta-D digestion. We interpret these results to mean that the 45,000 molecular mass form is a precursor with a signal peptide or transit sequence, and that the 43,000 molecular mass is the mature form of the protein.

Intracellular sites of the synthesis of sweet potato mitochondrial F1ATPase subunits

Five subunits (α-, β-, γ-, δ- and δ'-subunits) of the six α∼δ'-and ε-subunits) in the F1 portion (F1ATPase) of sweet potato (Ipomoea batatas) mitochondrial adenosine triphosphatase were isolated by an electrophoretic method. The δ- and δ'-subunits were not distinguishable immunologically but showed completely different tryptic peptide maps, indicating that they were different molecular species. In vitro protein synthesis with isolated sweet potato root mitochondria produced only the α-subunit when analyzed with anti-sweet potato F1ATPase antibody reacting with all the subunits except the ε-subunit. Sweet potato root poly(A)(+)RNA directed the synthesis of six polypeptides which were immunoprecipitated by the antibody: two of them immunologically related to the β-subunit and the others to the δ- and δ'-subunits. We conclude that the α-subunit of the F1ATPase is synthesized only in the mitochondria and the β-, δ- and δ'-subunits are in the cytoplasm.

Methylglyoxal bis(guanylhydrazone) elimination of polyamine effects on protein synthesis

The effect of methylglyoxal bis(guanylhydrazone) (MGBG), a structural analog of polyamines, on protein synthesis has been studied in the presence and absence of spermidine. The spermidine stimulation of polyphenylalanine- and MS2 RNA-directed RNA replicase synthesis in an Escherichia coli cell-free system and of globin synthesis in a rabbit reticulocyte cell-free system disappeared with the addition of MGBG. The spermidine reduction of misincorporation of leucine during polyphenylalanine synthesis in both E. coli and wheat germ cell-free systems was also disturbed by MGBG. MGBG noncompetitively interfered with polyamine stimulation of polyphenylalanine and globin synthesis, suggesting that MGBG could bind to both RNA and the complex of RNA and polyamine. MGBG was preferentially bound to ribosomal RNA among ribosomal RNA, poly(U), and calf thymus DNA, and strongly inhibited the amount of polyamine bound to ribosomal RNA. These results suggest that MGBG elimination of polyamine effects on protein synthesis may occur through the disturbance of polyamine binding to ribosomal RNA.

On the Role of Stored mRNA in Protein Synthesis in Embryonic Axes of Germinating Vigna unguiculata Seeds

Polyadenylated (poly A(+)) RNAs were prepared from both dry and incubated embryonic axes of Vigna unguiculata seeds and were translated by a wheat germ translation system. Analysis with gel electrophoresis and fluorography showed that translation products of poly A(+) RNA from dry embryonic axes were nearly the same as those from 2-hour incubated axes but somewhat different from those of 4- to 24-hour incubated axes, and that translation products remained almost unchanged between the 4- and 24-hour stages of postimbibition. The results indicate the possibility that the stored mRNA (poly A(+) RNA from dry embryonic axes) directs the protein synthesis required for early stages of germination. This is supported by comparison of the in vitro translation products of poly A(+) RNAs with those of polysomal RNAs. Experiments with alpha-amanitin, a specific inhibitor of RNA polymerase II (J. Jendrisak 1980 J Biol Chem 255: 8529-8533), suggested that the synthesis of some of the stored mRNA species is resumed as early as 4 hours after the onset of imbibition.

Hamster hepatic cytochrome b5: purifications, immunochemical properties, and in vitro synthesis

Cytochrome b5 has been purified from hamster liver microsomes. Both Ouchterlony double-diffusion and rocket immunoelectrophoresis experiments indicate that no immuno-cross-reactivity exists between guinea-pig anti-rabbit cytochrome b5 antibody and hamster cytochrome b5. However, anti-rabbit b5 IgG inhibited both hamster microsomal NADH-cytochrome c reductase and NADPH-dependent 7-ethoxycoumarin-O-deethylase activities. Hamster cytochrome b5 stimulated several reconstituted hamster cytochrome P-450-dependent monooxygenase activities and this stimulatory effect could be inhibited by antibody against rabbit cytochrome b5. Two-dimensional iodinated tryptic peptide mapping experiments provided evidence that the polypeptide fingerprint of hamster cytochrome b5 is substantially different from the fingerprints of cytochrome b5 isolated from rabbit, rat and bovine. We also studied the in vitro synthesis of hamster cytochrome b5 from liver mRNA using a wheat germ lysate system. A 16 kDa polypeptide, which is the same size as hamster cytochrome b5, was immunoprecipitated by antibody against rabbit b5. This experiment suggested that in vitro synthesized hamster cytochrome b5 is recognized by a heterologous antibody. Thus, hamster and rabbit cytochrome b5 do share some common immuno-determinants which may be located close to the heme-binding active site.