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

Induction of metallothionein mRNA in rat liver and kidney after copper chloride injection

The kinetics of the increase of metallothionein mRNA in rat liver and kidney after CuCl2 injection was determined by cell-free translation and dot-blot hybridization of total RNA isolated at various times after the injection. Both assay procedures gave essentially the same result: a 16-fold increase in hepatic metallothionein mRNA was observed 7h after CuCl2 injection, with a decline to basal values by 15 h. The response in the kidney was less dramatic, with a 6-fold increase in metallothionein mRNA 5 h after injection, and basal values were attained by 12h. The rise in Cu2+ concentration in both organs was closely correlated with the increase in metallothionein mRNA; hepatic Cu2+ was increased 5.9-fold by 5h after injection and renal Cu2+ was increased 4.3-fold 5h after injection. The Zn2+ concentration in the liver had not risen significantly within 5h of Cu2+ injection. Renal Zn2+ concentrations did not alter appreciably in the Cu2+-treated animals. These results support the conclusion that Cu2+ is acting as a primary inducer of metallothionein mRNA in the rat.

Isolation and characterisation of keratin mRNA from the scale epidermis of the embryonic chick

The keratin polypeptides of the epidermis from the leg scale region of 17-day-old embryonic chicks were extracted as S-carboxymethylated derivatives and characterised by electrophoresis on SDS and pH 9.5 urea gels including a combination of both in two dimensions. Proteins were isolated that gave X-ray diffraction patterns typical of alpha- and beta- (avian feather) keratins. An mRNA fraction was isolated from 17-day-old scale tissue by guanidinium chloride extraction and sucrose gradient fractionation. The mRNA was translated in the wheat germ system to give a major product indistinguishable from the molecular weight class (Mr 14 500) of scale beta-keratin polypeptides. A cDNA library was constructed in pBR322 from a 15 S mRNA subfraction and two recombinant clones were selected by their strong hybridisation to cDNA prepared from the 15 S mRNA. The sequencing of these has yielded details of the relatedness of two scale keratin genes including their 3' untranslated regions. Almost half of the protein sequences of the two homologous scale keratins has been deduced and a notable feature of the scale keratin structure appears to be the presence of at least two sequence domains consisting of 13 amino acid repeats.

Translational discrimination between the four RNAs of alfalfa mosaic virus. A quantitative evaluation

In an attempt to relate the translational characteristics of alfalfa mosaic virus (A1MV) RNAs to their structure [Ravelonandro et al. (1983) Nucleic Acids Res. 11, 2815-2826; Gehrke et al. (1983) Biochemistry 22, 5157-5164] we measured the relative affinities (discrimination ratios) of these RNAs for the initiation complex, in the wheat germ extract and in the nuclease-treated reticulocyte lysate, using a competition method designed by Brendler et al. [(1981) J. Biol. Chem. 256, 11747-11754]. As a prerequisite of this study we ascertained that the molecular mass distribution of the translation products was independent of RNA concentration in both translation systems. In the wheat germ extract the discrimination ratios are very similar for two strains of A1MV (S and B) which differ mainly by the presence (strain S) or absence (strain B) of a stable 5'-proximal hairpin. Hence this structure has no bearing on discrimination. Taking the affinity of RNA 3 as reference, the following orders of magnitude are found for the affinities of the different RNAs in the wheat germ: RNA 3, 1.0; RNA 1, 10; RNA 2, 60; RNA 4, 150. In the reticulocyte lysate the discrimination ratios are not significantly different from the wheat germ. Thus it seems that the mechanism of discrimination is essentially the same in the two translation systems, despite a difference in rate-limitation.

Nucleotide sequence of cloned cDNAs coding for preprosecapin, a major product of queen-bee venom glands

Total mRNA from queen-bee venom glands was transcribed into cDNA and cloned into the PstI and ClaI site of pBR322. The nucleotide sequence of two clones (pUM9/24 and pBMC1) with inserts derived from mRNAs for preprosecapin is presented. The two inserts, which are identical in their overlapping regions, have a coding region encompassing 77 triplets. The cloned cDNAs differ in the length of the 3'-untranslated region, which is about twice as long in clone pUM9/24. The postulated amino acid sequence of preprosecapin starts with a signal peptide containing an estimated 32 residues, followed by a pro part which terminates with a single arginine. The end-product secapin is located at the COOH end of the precursor. Activation of prosecapin must, therefore, differ from the processing of promelittin synthesized in the same gland. Cell-free translation of total venom gland mRNA in the presence of radioactive histidine yields only two major products, the smaller of which is presumably preprosecapin. Edman degradation of total translation products yields peaks of radioactive tyrosine and histidine at the 4th and 10th cycles respectively. This confirms the sequence of preprosecapin deduced from the cDNA clones. The content of secapin in queen-bee venom must be higher than it is in worker bee venom.

Thylakoid membranes: the translational site of chloroplast DNA-regulated thylakoid polypeptides

Stromal ribosomes and those bound to thylakoid membranes were prepared from intact spinach chloroplasts which were purified on Percoll gradients. The products of read-out translation of these ribosomes supplemented with an Escherichia coli extract were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Striking similarity was found between the polypeptides labeled in the read-out translation of the chloroplastic ribosomes and those synthesized in isolated chloroplasts. Among the polypeptides translated on thylakoid-bound ribosomes, apoprotein of chlorophyll-protein complex I, alpha and beta subunits of coupling factor 1, and 32,000-Da membrane polypeptide were identified from their mobility on the polyacrylamide gel. The large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase and other several stromal proteins were translated exclusively from stromal ribosomes. However, when the translation was programmed in cell-free systems from either E. coli, wheat germ, or rabbit reticulocytes by RNAs isolated separately from stroma and thylakoids, no qualitative difference was found between the products from those RNAs. These results suggest that thylakoid-bound ribosomes are the main sites of synthesis of thylakoid proteins and stromal-free ribosomes are that of stromal proteins, and that thylakoids and stroma contain mRNAs for the stromal and the thylakoid proteins, respectively, in a form not functioning in the chloroplasts.

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.

Pyruvate orthophosphate dikinase gene expression in developing wheat seeds

The amount of pyruvate orthophosphate dikinase (PPDK) (EC 2.7.9.1) protein in wheat (Triticum aestivum L. var Cheyenne) grains was determined at different stages of development by the protein blot method. The variation in PPDK protein with time in developing wheat grains was similar to that of the enzyme's activity reported by Meyer et al. (1982 Plant Physiol 69: 7-10). The variation in levels of PPDK mRNA with seed development was determined by analysis of polypeptides immunoprecipitated by anti-PPDK serum from in vitro translation products of extracted seed RNA. This mRNA variation was similar to that of the in vivo enzyme levels and the correlation is consistent with the regulation of PPDK gene expression by the level of its mRNA.The highest level of PPDK in developing wheat seeds occurs later than the highest levels of both ribulose bisphosphate carboxylase (EC 4.1.1.39) and of chlorophyll, which are located in the green pericarp tissue. PPDK was located in both endosperm and pericarp tissue of the seeds. The tissue location and developmental profile of seed PPDK are consistent with a metabolic role of providing phosphoenolpyruvate as a substrate for recapturing respiratory CO(2) in the seed, and possibly for amino acid interconversions during development.

Cloning and structure analysis of the rat apolipoprotein A-I cDNA

Apolipoprotein A-I, the major protein in mammalian high-density lipoprotein, acts as a cofactor for lecithin-cholesterol acyltransferase during the formation of cholesterol ester and as such, is thought to promote cholesterol efflux from peripheral cells to the liver. In this paper, we report the partial purification of rat liver apolipoprotein A-I mRNA by a polysome immunoadsorption technique, and its cDNA cloning. Isolation of two overlapping cDNA clones enabled us to derive the whole rat apolipoprotein A-I cDNA coding sequence. Comparison of the deduced protein sequence with its human counterpart reveals a striking homology between the prepropeptide precursors. Both mature protein amino-terminal regions are very homologous, suggesting that this particular domain could be involved in lipid/protein binding or lecithin-cholesterol acyltransferase activation.

Developmental regulation, induction, and embryonic tissue specificity of sea urchin metallothionein gene expression

Metallothionein (MT) is shown to be present in sea urchin embryos on the basis of its characteristic properties as a small protein (6-7 Da) of extraordinarily high cysteine content, whose biosynthesis is readily induced by heavy metals. Induction by Zn2+ results in the accumulation of the cysteine-rich MT protein, a 0.8 kb MT mRNA and a 2.9 kb nuclear RNA. The amount of MT mRNA is regulated intrinsically through the course of embryogenesis to the pluteus stage: A maternal MT mRNA is poly(A)-deficient and is polyadenylated after fertilization. New MT mRNA begins to accumulate between the seventh and eighth cell cleavage, reaches a maximum at the mesenchyme blastula stage, decreases during gastrulation, and rises again in the early pluteus stage. "Animalizing" embryos with Zn2+ during early embryogenesis causes a sustained accumulation of MT mRNA to levels greater than 25 times the normal amount. MT mRNA is present in high amount in the ectoderm of the pluteus, but is barely detectable in the mesoderm-endoderm tissue fraction. Treatment of either the pluteus or its isolated tissue fractions with Zn2+ results in the induction of MT mRNA accumulation in the mesoderm-endoderm but not in the already MT mRNA-enriched ectoderm. Furthermore, differences in Zn2+ induction of the MT gene in the blastula and gastrula are consistent with a developmental pattern in which MT gene expression is maintained constitutively at a high level in the ectoderm and at a low level in the mesoderm-endoderm tissues, which are, however, preferentially inducible by Zn2+.

Polyadenylated mRNA from the photosynthetic procaryote Rhodospirillum rubrum

Total cellular RNA extracted from Rhodospirillum rubrum cultured in butyrate-containing medium under strict photosynthetic conditions to the stationary phase of growth has been fractionated on an oligodeoxythymidylic acid-cellulose column into polyadenylated [poly(A)+] RNA and poly(A)- RNA fractions. The poly(A)+ fraction was 9 to 10% of the total bulk RNA isolated. Analysis of the poly(A)+ RNA on a denaturing urea-polyacrylamide gel revealed four sharp bands of RNA distributed in heterodisperse fashion between 16S and 9S. Similar fractionation of the poly(A)- RNA resulted in the separation of 23, 16, and 5S rRNAs and 4S tRNA. Poly(A)+ fragments isolated after combined digestion with pancreatic A and T1 RNases and analysis by denaturing gel electrophoresis demonstrated two major components of 80 and 100 residues. Alkaline hydrolysis of the nuclease-resistant, purified residues showed AMP-rich nucleotides. Through the use of snake venom phosphodiesterase, poly(A) tracts were placed at the 3' end of poly(A)+ RNA. Stimulation of [3H]leucine incorporation into hot trichloroacetic acid-precipitable polypeptides in a cell-free system from wheat germ primed by the poly(A)+ RNA mixture was found to be 220-fold higher than that for poly(A)- RNAs (on a unit mass basis), a finding which demonstrated that poly(A)+ RNAs in R. rubrum are mRNAs. Gel electrophoretic analysis of the translation mixture revealed numerous 3H-labeled products including a major band (Mr, 52,000). The parent protein was precipitated by antibodies to ribulose bisphosphate carboxylase-oxygenase and comprised 6.5% of the total translation products.

In vitro translation of infectious flacherie virus RNA in a wheat germ and a rabbit reticulocyte system

Infectious flacherie virus is an insect picornavirus isolated from the silkworm, Bombyx mori. Its RNA was found to act as an efficient mRNA in a wheat germ extract and a rabbit reticulocyte lysate translation system. In either system the sum of molecular weights of translation products far exceeded the coding capacity of the virus genome, which suggests the occurrence of proteolytic cleavage of large primary products to smaller polypeptides as reported for other picornaviruses and/or premature termination of translation. The highest molecular weight product of 200 000 (polyprotein-like product) could be translated in both systems. One of the antigenic products common to both systems had a molecular weight of 130 000, which corresponds to the sum of molecular weights of the four major viral proteins. Another product, which comigrated with viral protein 0, the largest viral structural protein in SDS-polyacrylamide gel electrophoresis, also showed antigenicity. Peptide mapping of these polypeptides showed that the two in vitro systems translated the same cistron in the viral RNA and that the smaller polypeptide was a part of the 130 000 Da product.

In vitro translation of distinct mRNAs coding for the precursors of porcine LH subunits

Conditions are described to characterize and estimate the precursors of porcine LH alpha and beta subunits and indirectly their specific mRNAs. Poly(A) RNAs extracted from castrated male pig anterior pituitaries were translated in a wheat-germ system in the presence of [35S] cysteine and [35S] methionine. The translation products were precipitated by antisera directed against reduced and carboxymethylated LH alpha and beta subunits and analyzed by high resolution electrophoresis. It is shown that the precursors of pLH alpha and beta subunits are located in two distinct congruent to 15 K proteins and represent--on the basis of the incorporation of the [35S] labeled aminoacids into proteins--congruent to 0.12% and 0.05% respectively of the total translation products. It is suggested that in the pig, as in other species, the LH alpha and beta subunits are encoded by two distinct mRNAs, and at variance with other species the leader sequence of LH alpha mRNA is longer than that of LH beta mRNA.

Changes in hamster liver albumin synthesis during the development of cardiomyopathy

Control ( F1B ) and cardiomyopathic (Bio 14.6) hamsters have been studied over an 11 month time interval, in an attempt to relate alterations in liver function with the onset of progressive heart damage. In most instances the parameters measured (e.g., liver weight, liver polysome content, in vitro polysome driven protein synthesis) were similar for both groups of animals. The exceptions appeared to be two Bio 14.6 animals that had liver hypertrophy, coupled with severe necrosis and liver damage. These livers had very low levels of virtually inactive polysomes and depicted many of the histopathological characteristics of hepatic ischemic injury known in humans to be associated with congestive heart failure. Our biochemical and histological data suggests that for the Bio 14.6 hamsters, progressive cardiomyopathy is associated with severe liver damage for only a few animals.

Ribonucleic Acid and protein metabolism in pea epicotyls : I. The aging process

Aging of actively growing, etiolated pea Pisum sativum L. var Alaska plants was initiated by removing the plumules of plants in the third internode stage, and applying lanolin to the cut apices of otherwise intact plants. During the subsequent 4-day aging period, several degenerative events occurred in this apical 10-millimeter region. Ribosomal RNA and messenger RNA contents declined, polyribosomes disaggregated, and the protein synthesizing capacity of the polysomes decreased.Two-dimensional, silver-stained protein patterns revealed that aging altered the relative amounts of specific cellular proteins accumulated in vivo. In addition, polypeptide patterns generated by cell-free translation of total and polysomal RNA, isolated from unaged and aged tissues, showed major modifications. More than 200 spots could be resolved by two-dimensional gel fluorography of translation products using RNA from fresh tissues. Of these 200 spots, about eight appeared or increased when total RNA from aged tissue was used, and about 58 disappeared or declined. When polysomal RNA from aged tissue was used as template, about 12 spots appeared or increased, whereas about 64 disappeared or decreased. In general, the products which increased after aging were lower molecular weight and those that decreased were higher molecular weight.

Biosynthesis of the ubiquinol-cytochrome c reductase complex in yeast. Characterization of precursor forms of the 44-kDa, 40-kDa and 17-kDa subunits and identification of individual messenger RNAs for these and other imported subunits of the complex

The mitochondrial ubiquinol--cytochrome c reductase complex (complex III or cytochrome bc1 complex) is thought to consist of eight subunits, seven of which are specified by nuclear genes and synthesized in the cytoplasm. We have studied the synthesis of five of the nuclear-encoded subunits both in vivo and in vitro and show that of these the 44-kDa, 40-kDa and 17-kDa subunits are synthesized with cleavable extensions, while the 14-kDa and 11-kDa proteins are synthesized without detectable extra sequences. The sizes of the pre-sequences, as determined by the relative mobility of the precursor proteins in sodium dodecyl sulphate/polyacrylamide gels, range from 0.5-kDa for the 44-kDa and 40-kDa subunits to 9-kDa for the 17-kDa subunit. The existence in vivo of precursor forms to the 44-kDa, 40-kDa and 17-kDa subunits implies that import is at least partially a post-translational process. The precursor of the 44-kDa subunit can be processed post-translationally in vitro by isolated mitochondria. The messenger RNAs for subunits of the complex have been studied. Those coding for the 44-kDa, 40-kDa, 14-kDa and 11-kDa proteins and cytochrome c1 are of different sizes, indicating that each of these subunits is synthesized as a separate protein, rather than as part of a polyprotein precursor.

Phytoferritin is synthesized in vitro as a high-molecular-weight precursor. Studies on the synthesis and the uptake in vitro of the precursors of ferritin and ferredoxin by intact chloroplasts

Evidence is presented that French-bean (Phaseolus vulgaris) seed ferritin is composed of one type of subunit with an apparent Mr of 26500. In normal and iron-loaded leaf tissues it is detected immunologically with an antiserum raised against purified bean seed ferritin and migrates in SDS (sodium dodecyl sulphate)/polyacrylamide-gel electrophoresis with the same mobility as the bean seed ferritin subunit. The biosynthetic pathway of ferritin in normal and iron-loaded leaves was investigated. RNA was extracted, fractionated into polyadenylated RNA and translated in a cell-free rabbit reticulocyte lysate and a wheat-germ-extract system. The products were identified by SDS/polyacrylamide-gel electrophoresis after indirect immunoprecipitation. In all cases the ferritin product had an Mr 5000 higher than that of the native subunit. Uptake and processing of the precursor form of ferritin from iron-loaded leaves by intact chloroplasts was demonstrated. This indicates that, in iron-loaded leaves, ferritin acts as a chloroplast protein. We propose that the ferritin precursor in normal leaves follows the same biosynthetic pathway. This suggests that the iron-buffering function of ferritin in plants takes place in the chloroplast and that non-functional cellular iron will accumulate in this cell organelle.

Timing and rates of synthesis of early histone mRNA in the embryo of Strongylocentrotus purpuratus

The level of early histone mRNA in Strongylocentrotus purpuratus changes abruptly at 6 hr of development, increasing an average of 10-fold by 9-10.5 hr and then decreasing over 2-fold by 13.5-15 hr. These changes occur when the late embryonic mRNA is still a very minor component of histone gene transcription. The exact values of increase and decrease of mRNA level vary from experiment to experiment and may reflect the conditions of embryos at different times. The instantaneous rate of synthesis of histone RNA per embryo increases from at least 47 fg/min at 6 hr to 114 fg/min at 9 hr and then drops to 29 fg/min at 12 hr. The rate of mRNA accumulation is lower: 20, 43, and 12 fg/min, respectively. On a per cell basis, however, the rate of synthesis and accumulation is highest at 6 hr and continuously decreases to 1/20 the level per cell at 12 hr. The transcriptional rates and relative mRNA increases taken together predict an average increase from 0.16 to 0.24 pg/embryo (6-10 X 10(5) molecules) per mRNA species in the egg to 1.6 to 2.4 pg/embryo (6-10 X 10(6) molecules) at 10.5 hr. The transcription rates indicate that at the maximal values we obtained, about two to three molecules of each histone RNA are made per gene copy per minute. The half-life of the histone mRNAs in the period from 6 to 13.5 hr probably varies, with the maximal turnover at about the time histone RNA level peaks. A half-life of 1.5 hr at 12 hr of development is estimated. Change in transcriptional rate per nucleus, increase in cell number, and probably a change in mRNA stability as well are therefore involved in the control of histone mRNA levels in the early embryo.

Regulation of maltase synthesis in Saccharomyces carlsbergensis

The induction of maltase (EC 3.2.1.20) by its inducer maltose in a strain of the yeast Saccharomyces carlsbergensis carrying a functional MAL locus is regulated at the level of transcription. Preceding the synthesis of increased levels of maltase is the de novo synthesis of maltase-specific RNA sequences. This was detected by determining the level of maltase mRNA by DNA-RNA hybridizations by using a maltase structural gene DNA sequence probe and by assaying functional maltase mRNA by in vitro RNA-directed synthesis of immunologically reactive maltase. Once maltase has accumulated, late in induction, further synthesis of the enzyme is inhibited, as reflected by reduced levels of the mRNA that encodes maltase.

Cell-free synthesis of succinate dehydrogenase and mitochondrial adenosine triphosphatase of sweet potato

Polyadenylated mRNA was isolated from aged slices of sweet potato root tissue and translated in a wheat germ cell-free system. The synthesis of apoprotein of the flavoprotein subunit of succinate dehydrogenase and two of the subunits of mitochondrial adenosine triphosphatase were detected by indirect immunoprecipitation. The molecular weights of the immunologically identified products were 3,000 and 8,000-9,000 daltons larger than the mature flavoprotein subunit of succinate dehydrogenase and the mature subunits of adenosine triphosphatase, respectively.

In vitro synthesis of biologically active human leukocyte interferon in a RNA-dependent system from Saccharomyces cerevisiae

RNA isolated from yeast Saccharomyces cerevisiae containing recombinant plasmid DNA coding for a human leukocyte interferon gene was used as template in a modified yeast cell-free translation system. Radioactive as well as biologically active leukocyte interferon was synthesized.

Quantitative changes in in vitro and in vivo protein synthesis in aging and rejuvenated soybean cotyledons

Cotyledons of light-grown soybean (Glycine max L. var Wayne) seedlings were used as a model system to study the possibility that aging requires qualitative changes in protein synthesis. Cotyledons reached a final stage of senescence and then abscised about 22 days after imbibition. Cotyledon senescence was reversed at 20 days after germination by epicotyl removal. Thereafter, the cotyledons regained much of the chlorophyll, RNA, protein, and polyribosomes lost during aging.Total poly(A)mRNA was extracted from 4-, 12-, 20-day-old, and rejuvenated cotyledons and translated in a wheat germ system. Comparison of translation products on two-dimensional O'Farrell gels showed that many translation products increased in quantity during aging, while roughly half as many decreased. Rejuvenation returned the translation products to approximately 4-day-old levels in roughly half of those products which were diminished with age. Conversely, almost one-third of the products which had increased with age decreased with rejuvenation. None of the translation products were totally lost nor were newly synthesized products detected during aging. Therefore, aging in this system probably does not involve complete gene repression or depression. The observation that epicotyl removal causes a reversal in the levels of various proteins synthesized in vitro was corroborated by similar observations following in vivo labeling of cotyledon sections and analysis by SDS-polyacrylamide gel electrophoresis and fluorography. Densitometric scans of fluorograms revealed a gradual shift in profiles of both in vitro and in vivo translation products during aging. Rejuvenated cotyledon proteins had a profile resembling that of 4-day-old cotyledons. The overall level of [(35)S]methionine incorporation into protein in vivo declined gradually during aging but was restored to 4-day-old levels within 2 days after epicotyl removal.

In vivo and in vitro synthesis of CM-proteins (A-hordeins) from barley (Hordeum vulgare L.)

CM-proteins from barley endosperm (CMa, CMb, CMc, CMd), which are the main components of the A-hordein fraction, are synthesized most actively 10 to 30 d after anthesis (maximum at 15-20 d). They are synthesized by membranebound polysomes as precursors of higher apparent molecular weight (13,000-21,000) than the mature proteins (12,000-16,000). The largest in vitro product (21,000) is the putative precursor of protein CMd (16,000), as it is selected with anti-CMd monospecific IgG's, and is coded by an mRNA of greater sedimentation coefficient (9 S) than those encoding the other three proteins (7.5 S). CM-proteins always appear in the soluble fraction, following different homogenization and subcellular fractionation procedures, indicating that these proteins are transferred to the soluble fraction after processing.

Perturbation of the mitochondrial lysine tRNA population by virus-induced transformation or stress of mammalian cells: functional properties and nucleotide sequence of a mitochondrially associated lysine tRNA

Eleven isoaccepting lysine tRNAs from mammalian sources are demonstrable by RPC-5 chromatography and polyacrylamide gel electrophoresis. The appearance and amounts of these isoacceptors varies with the source and growth state of cells. One isoacceptor, tRNALys6, observed in preparations of tRNA from some virus-transformed cells in culture, has been characterized by determining functional properties, cellular location, and its nucleotide sequence. tRNALys6 responds primarily to the lysine codon AAA, but it is not used efficiently in a wheat germ translational system in vitro. Compared with lysine isoacceptors 1, 2, 4, 5a, and 5, [3H]lysine appears in vivo in tRNALys6 with a delay of about 3 h. This delay may in part be a result of a less functional tRNA, but a compartmented state of tRNALys6 also appears to be important. tRNALys6 is associated with mitoplasts prepared from KA31 fibroblasts. The nucleotide sequence of tRNALys6 was determined by rapid postlabeling procedures involving limited hydrolysis in formamide, 32P-labeling of 5' ends of fragments with polynucleotide kinase, separation of the nested set of fragments in polyacrylamide denaturing gels, release of 5'-labeled nucleotides with RNase T2, and identification of the released nucleotides by chromatography on PEI cellulose. Confirmation of the positions of major nucleotides was done by using limited digestions by RNases of tRNALys6 labeled with 32P on the 3' terminus in a gel readout procedure. The nucleotide sequence of tRNALys6 differs from that of cytoplasmic lysine tRNAs and mammalian mitochondrial lysine tRNAs. It contains U*, an unidentified modified uridine occurring in the anticodon of some mitochondrial tRNAs. tRNALys6 appears to occur in very limited amounts, or not at all, in most cells unless stressed, but when present it is associated with mitochondria, although it is probably coded in the nucleus.

Small nuclear RNAs and translation

The possibility that small nuclear RNA species U1 might be involved in the inhibition of protein synthesis that occurs during mitosis has been explored. Upon exposure of mitotic HeLa cell extracts to 1% sodium deoxycholate, the majority of the rapidly sedimenting U1 RNA shifted to lower sedimentation rates. This suggests that it is associated with heterogeneous nuclear RNA ribonucleoprotein particles, instead of a ribosomal population. Erythrocyte ghost-mediated microinjection of anti-(U1)RNP antibodies into synchronized HeLa cells did not prevent the suppression of protein synthesis that is observed under mitosis. Examination of the published nucleotide sequences of U1 and U2 RNA suggests that these RNA species could potentially code for some short peptides. When purified U1 or U2 RNA were added to cell-free polypeptide synthesizing systems, the synthesis of these peptides was not detected.

Expression of a prokaryotic gene in yeast: isolation and characterization of mutants with increased expression

The Escherichia coli Tn9 derived chloramphenicol resistance gene (camr) is functionally expressed in the yeast Saccharomyces cerevisiae. This gene was introduced into yeast cells as part of a hybrid yeast/E. coli shuttle plasmid. A number of plasmid associated yeast mutants overproducing the camr gene product, chloramphenicol acetyltransferase (acetyl-CoA: chloramphenicol 3-0-acetyltransferase, E.C. 2.3.1.28) were isolated. One of the plasmid mutants was analyzed in some detail. Even though this mutant showed a 1,000 fold overproduction of chloramphenicol acetyltransferase in the yeast host the level of RNA complementary to the camr gene was not increased. A deletion of 127 base pairs in the region immediately upstream from the 5' end of the camr gene appeared to be responsible for the "up" phenotype of this mutant. This mutation affected the expression of the camr gene in E. coli in a "down" fashion, in contrast to its effect in yeast.

Isolation and characterization of nuclear genes coding for subunits of the yeast ubiquinol-cytochrome c reductase complex

Nuclear genes coding for the Mr 17 000, 14 000 and 11 000 subunits of the ubiquinol-cytochrome c reductase complex (complex III) in yeast have been isolated from a clone bank of yeast nuclear DNA by use of a mRNA hybridization-competition assay. This is based on our observations that levels of mRNAs for these subunits are much reduced during glucose repression and in cytoplasmic petite mutants and the procedure should be of general application for the isolation of other inducible or repressible genes coding for mRNAs present at low levels in the cell. A first characterization of the clones is presented. The genes are not closely linked in the genome and those coding for Mr 14 000 and 11 000 subunits are present in unique genomic environments, which suggests that there are only single copies of each in the nuclear genome.

Separation and characterization of low-molecular-weight nuclear RNA species that inhibit cell-free protein synthesis

Various RNA fractions were isolated from nuclei of 12-day lactating rat mammary glands and examined for their ability to inhibit cell-free protein synthesis. Although total nuclear RNA was generally inactive, material contained in the poly(A)+ nuclear RNA fraction and the low-molecular-weight RNA derived from total nuclear RNA by sucrose gradient centrifugation, inhibited the translation of several mRNAs but not poly(U) or poly(A). Separation of the small nuclear RNAs by preparative polyacrylamide-urea gel electrophoresis allowed the identification of at least three active inhibitor RNA species. These differed both with respect to their ability to inhibit protein synthesis, and in their mechanism of action. While two of the RNA species inhibited elongation the other inhibited initiation of protein synthesis.

Increase of fidelity of polypeptide synthesis by spermidine in eukaryotic cell-free systems

The mechanism of spermidine-induced increase of fidelity of polypeptide synthesis in a wheat germ cell-free system has been studied. It was found that the increase of fidelity in the presence of spermidine occurred mainly at the level of binding of aminoacyl-tRNA to ribosomes, that reduction of misreading was more marked at the 5'-base than at the 3'-base of the codon and that misreading caused by paromomycin and kanamycin C was not significantly decreased by spermidine. It was deduced from these results that spermidine inhibited low-frequency misreading more strongly than high-frequency misreading. In addition, spermidine was found to stimulate the rejection of non-cognate aminoacyl-tRNA mainly at an initial discrimination step during the binding of amino-acyl-tRNA to ribosomes, and slightly at a subsequent GTP-dependent discrimination step, the so-called proofreading step. In yeast, rabbit reticulocyte, and Artemia salina cell-free systems, spermidine was found to increase the fidelity of protein synthesis.

In vitro synthesis of M and Z forms of human alpha 1-antitrypsin

mRNA was prepared from autopsy liver samples from a homozygote for alpha 1-antitrypsin deficiency (PiZZ) and from a normal (PiMM) subject. Both preparations gave equivalent synthesis of alpha 1-antitrypsin in a wheat germ cell-free system. This suggests that the deficiency of plasma alpha 1-antitrypsin associated with the Z variant is due to a failure of processing and secretion of the protein rather than of its synthesis. It is likely that it is the resultant intracellular accumulation of the Z protein rather than a deficiency of protease inhibitor that is the primary cause of the liver pathology associated with this variant.

In vitro synthesis of lectins in cell-free extracts from dry wheat and rye embryos

Cell-free extracts from dry wheat (Triticum vulgare L.) and rye (Secale cereale L.) embryos do not synthesize their corresponding lectins when incubated under conditions optimalized for translation of either exogenous or endogenous mRNA. Only when the extracts are prepared and incubated in the complete absence of sulphydryl containing compounds lectins are synthesized in vitro. Since immunoprecipitation techniques could not demonstrate unequivocally the presence of lectin among the cell-free translation products a specific affinity purification procedure has been developed in order to proof the presence of stored lectin mRNAs in dry wheat and rye embryos.

The effect of high hydrostatic pressure on eukaryotic protein synthesis

The pressure response of two eukaryotic protein synthesizing systems has been characterized. The rabbit reticulocyte system has been tested, both in vivo and in vitro, using endogenous polysomes and polyuridylic acid (poly U). In addition, the poly U-directed polyphenylalanine synthesizing system obtained from wheat germ was utilized. The effect of pressure on eukaryotic protein synthesis has been found to be basically similar to that observed in prokaryotic systems, although the response of the eukaryotic protein synthesizing system is somewhat more complex signifying a greater influence of overlapping reactions. Magnesium was found to affect eukaryotic systems in much the same way as has been reported for prokaryotic systems, i.e., increasing the Mg2+ concentration in a protein synthesizing system increases the barotolerance exhibited by the system. Under conditions of high Mg2+ concentration, however, extreme (up to 160%) stimulation of protein synthesis at lower pressure levels was observed in the eukaryotic systems. Such high stimulation is not apparent in prokaryotic systems. The poly U-directed wheat germ system exhibited the most barotolerant polypeptide synthesis ever seen in our laboratory. This extreme barotolerance was only slightly decreased when the system was tested at reduced concentrations of magnesium.

Cell-free synthesis of phytochrome apoprotein

A single polypeptide is immunospecifically precipitated by monospecific antiphytochrome from the total translation products of both wheat-germ and rabbit-reticulocyte cell-free protein synthesizing systems programmed with oat (Avena sativa L.) poly(A) RNA. The mobility of this polypeptide is slightly lower on sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis than that of immunoaffinity-purified, 118 kdalton phytochrome and corresponds to an apparent molecular weight of 124 kdalton. Evidence against the possibility that this mobility difference results from intracellular processing of the 124-kdalton protein is provided by extraction of freeze-dried tissue directly into boiling SDS-containing buffer. This procedure yields a phytochrome species with a mobility on SDS polyacrylamide gel electrophoresis indistinguishable from that of the in-vitro translation product. Together the data indicate that the phytochrome polypeptide is synthesized in its mature form in the cell but is subject to modification to a form with lower apparent molecular weight during immunopurification.

The quantitation of liver cytochrome P450-LM2 mRNA in rabbits of different ages and after phenobarbital treatment

Using very young (neonate or 0 day), 50-, 100-, 300- and 830-day-old rabbits we have studied changes in liver drug-metabolizing activities. Total liver microsomal cytochrome P450 content, benzphetamine N-demethylase and 7-ethoxycoumarin O-deethylase activities all decline with increasing age. When the rabbits of different age groups were pretreated with phenobarbital, liver microsomal enzyme activities increased in each group as compared with its control, but the total induced activities still decreased with increasing age. Using a specific assay for translatable cytochrome P450-LM2 mRNA, we show that the age-dependent decrease in control and phenobarbital-induced enzyme activities is due to a decrease in the levels of translatable mRNA specific for cytochrome P450-LM2. This is the first report on an age-dependent decrease in the level of a specific translatable mRNA. We do not know whether this decrease is due to decreased mRNA synthesis, or increased mRNA degradation.

Analysis of revertants of a ribosomal mutation in Podospora anserina: evidence for new ribosomal mutations which confer hypersensitivity to paromomycin

This paper describes the analysis of cold-resistant revertants of a cold-sensitive mutant. Pm1-1 is a ribosomal mutation screened for its paromomycin resistance. Suppression of its cold sensitivity occurs with two kinds of external mutations localized in two different loci. One of them, PmB, is assumed to be a ribosomal gene. PmB mutations confer hypersensitivity to paromomycin in vivo as well as in vitro in a cell-free protein synthesis system.