Expression of three Trichoderma reesei cellulase genes in Saccharomyces pastorianus for the development of a two-step process of hydrolysis and fermentation of cellulose

AIMS

To compare the production of recombinant cellulase enzymes in two Saccharomyces species so as to ascertain the most suitable heterologous host for the degradation of cellulose-based biomass and its conversion into bioethanol.

METHOD AND RESULTS

cDNA copies of genes representing the three major classes of cellulases (Endoglucanases, Cellobiohydrolases and β-glucosidases) from Trichoderma reesei were expressed in Saccharomyces pastorianus and Saccharomyces cerevisiae. The recombinant enzymes were secreted by the yeast hosts into the medium and were shown to act in synergy to hydrolyse cellulose. The conditions required to achieve maximum release of glucose from cellulose by the recombinant enzymes were defined and the activity of the recombinant enzymes was compared to a commercial cocktail of T. reesei cellulases.

CONCLUSIONS

We demonstrate that significantly higher levels of cellulase activity were achieved by expression of the genes in S. pastorianus compared to S. cerevisiae. Hydrolysis of cellulose by the combined activity of the recombinant enzymes was significantly better at 50°C than at 30°C, the temperature used for mesophilic yeast fermentations, reflecting the known temperature profiles of the native enzymes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results demonstrate that host choice is important for the heterologous production of cellulases. On the basis of the low activity of the T. reesei recombinant enzymes at fermentation temperatures, we propose a two-step process for the hydrolysis of cellulose and its fermentation into alcohol using cellulases produced in situ.

A novel spectrofluorometric microassay for Streptococcus mutans adherence to hydroxylapatite

Adherence to the tooth surface by Streptococcus mutans is an important step in initiation of dental caries. Current in vitro methods used to study bacterial adherence are time-consuming and may involve the use of radiolabels. The aim of this study was to develop a more convenient, high-throughput, microtitre-plate assay of bacterial adherence to hydroxylapatite. S. mutans was labelled with the fluorescent indicator BCECF/AM and fluorescence measured using a spectrofluorometer. Fluorescence microscopy confirmed label uptake. Optimal labelling occurred at 120 min with 50 microM BCECF/AM in DMSO. Viability was similar in control untreated bacterial cells, bacteria treated with DMSO alone or with the label for up to 4 h. Preliminary adherence experiments were performed using four commercially available types of hydroxylapatite. Fluorescence from pre-labelled bacteria was measured for bound cells. The assay was then optimised with respect to time and bacterial concentration using Fluka crude hydroxylapatite. Time course studies demonstrated that adherence reached saturation by 30 min incubation when using 1x10(7) cfu/ml labelled bacteria to 1 mg hydroxylapatite, coated with PBS or saliva. The fluorescence-based adherence assay was highly reproducible in repeated analyses and was useful in demonstrating interference with adherence. In conclusion, this microtitre-plate assay offers a more convenient approach to examine streptococcal adherence and could be used to screen for potential anti-adhesive agents.

Transcription profile of brewery yeast under fermentation conditions

AIMS

Yeast strains, used in the brewing industry, experience distinctive physiological conditions. During a brewing fermentation, yeast are exposed to anaerobic conditions, high pressure, high specific gravity and low temperatures. The purpose of this study was to examine the global gene expression profile of yeast subjected to brewing stress.

METHODS AND RESULTS

We have carried out a microarray analysis of a typical brewer's yeast during the course of an 8-day fermentation in 15 degrees P wort. We used the probes derived from Saccharomyces cerevisiae genomic DNA on the chip and RNA isolated from three stages of brewing. This analysis shows a high level of expression of genes involved in fatty acid and ergosterol biosynthesis early in fermentation. Furthermore, genes involved in respiration and mitochondrial protein synthesis also show higher levels of expression.

CONCLUSIONS

Surprisingly, we observed a complete repression of many stress response genes and genes involved in protein synthesis throughout the 8-day period compared with that at the start of fermentation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This microarray data set provides an analysis of gene expression under brewing fermentation conditions. The data provide an insight into the various metabolic processes altered or activated by brewing conditions of growth. This study leads to future experiments whereby selective alterations in brewing conditions could be introduced to take advantage of the changing transcript profile to improve the quality of the brew.

Dynamic changes in small nuclear ribonucleoproteins of heat-stressed and thermotolerant HeLa cells

Living organisms when subjected to various forms of environmental stress mount a physiological response to survive the long- and short-term ill-effects of the stress. The stress response may involve selective shut down of non-essential metabolic activities and the repair of macromolecular damage resulting from the stress. Messenger RNA splicing in cultured HeLa cells is one of the processes inhibited by heat stress. Splicing is protected from such inhibition in stress-preconditioned cells that have acquired a tolerant state characterised by increased cell survival and resistance to other environmental stresses. Stress tolerant cells have heat shock proteins (HSPs) that had been induced by the preconditioning process. To examine the biochemical changes induced by stress in the splicing apparatus, we analysed the small nuclear ribonucleoprotein (snRNP) particles associated with spliceosomes in normal, stressed, and stress tolerant cells. We show that (a) the spliceosomal component U4/U5/U6 snRNP particle is disassembled by heat stress into intermediates of splicing assembly, (b) prior induction of stress tolerance protects the structural and functional integrity of snRNPs if cells are subsequently exposed to a severe stress and (c) a novel 65 kDa protein is associated with small nuclear ribonucleoprotein particles in stress tolerant cells.

The stress response is repressed during fermentation in brewery strains of yeast

Yeast cells encounter a variety of environmental stresses during brewing and must respond to ensure cell survival. Cells can respond to stress by inducing a Heat Shock Response in which heat shock proteins (Hsps) are synthesized. In laboratory strains of Saccharomyces cerevisiae, the heat shock protein, Hsp104, plays a major role in the acquisition of tolerance to a variety of stresses such as heat, ethanol and sodium arsenite, and as such acts as an excellent stress indicator. The induction of Hsp104 in bottom-and top-fermenting brewery strains was examined when grown under laboratory and industrial fermentation conditions, and it was found that each brewing strain exhibits its own unique pattern of Hsp104 expression. During industrial fermentations, brewery strains are capable of mounting a stress response at the early stages of fermentation. However, as the fermentation proceeds, the response is repressed. The results suggest that conditions experienced in industrial brewing prevent the activation of the stress response. This study increases our understanding of alterations in gene expression patterns during the brewing process, and yields information that will aid in the definition of best practice in yeast management.

The paternal allele of the H19 gene is progressively silenced during early mouse development: the acetylation status of histones may be involved in the generation of variegated expression patterns

Transcriptional silencing can reflect heritable, epigenetic inactivation of genes, either singly or in groups, during the life-time of an organism. This phenomenon is exemplified by parent-of-origin-specific inactivation events (genomic imprinting) for a subset of mammalian autosomal genes, such as H19. Very little is known, however, about the timing and mechanism(s) of silencing of the paternal H19 allele during mouse development. Using a novel in situ approach, we present evidence that the silencing of the paternal H19 allele is progressive in the trophectodermal lineage during early mouse development and generates variegated expression patterns. The silencing process apparently involves recruitment of histone deacetylases since the mosaic paternal-specific H19 expression reappears in trichostatin A-treated mouse conceptuses, undergoing in vitro organogenesis. Moreover, the paternal H19 alleles of PatDup.d7 placentas, in which a region encompassing the H19 locus of chromosome 7 is bipaternally derived, partially escape the silencing process and are expressed in a variegated manner. We suggest that allele-specific silencing of H19 share some common features with chromatin-mediated silencing in position-effect variegation.

Bridging student health risks and academic achievement through comprehensive school health programs

In the National Action Plan for Comprehensive School Health Education, representatives for over 40 health, education, and social service organizations viewed education and health as independent systems. Participation concluded that healthy children learn better, and they cautioned that no curriculum can compensate for deficiencies in student health status. While literature confirms the complexity of health issues confronting today's students, schools face enormous pressure to improve academic skills. Local school leaders and stakeholders often remain unconvinced that improving student health represents a means to achieving improved academic outcomes. A rich body of literature confirms a direct link between student health risk behavior and education outcomes, education behavior, and student attitudes about education. This article summarizes relevant information concerning the health risk behavioral categories of intentional injuries; tobacco; alcohol, and other drugs; dietary, physical activity, and sexual risk behaviors.

Highly repetitive structure and its organization of the silk fibroin gene

We have sequenced a number of cDNAs representing the Bombyx mori silk fibroin heavy chain transcript. These reveal that the central region of the fibroin gene is composed of alternate arrays of the crystalline element a and the noncrystalline element b. The core region is partitioned by a homogeneous nonrepetitive amorphous domain of around 100 bp in length. The element a is characterized by repeats of a highly conserved 18-bp sequence coding for perfect repeats of the unit peptide Gly-Ala-Gly-Ala-Gly-Ser. The element b is composed of repeats of a less-conserved 30-bp sequence which codes for a peptide similar to that in element a except in that (1) Ser is replaced by Tyr and (2) there are irregular substitutions of Ala to Val or Tyr. Therefore, the structure of the fibroin gene core consists of three-step higher-order periodicities. Heterogeneities in numbers of repeats are observed in each step of periodicity. Boundary sequence appeared in each periodicity to be quite homogeneous. Sequence analysis indicates that the unit sequences of elements a and b have homology to those of recombination hotspots reported in other genes and a recombination event may frequently occur between the misaligned sister chromatids, resulting in heterogeneities in repeat numbers and duplication or deletion of repetitive sequences. The repetitive superstructure of the fibroin gene may have been a result of continuous unequal crossovers in a primordial gene during evolution. A couple of important features of the fibroin protein were proved by the present nucleotide sequencing.(ABSTRACT TRUNCATED AT 250 WORDS)

The results of 20 years of family practice residency training at the University of Louisville

In response to shortages of generalist physicians, especially in rural areas, family practice residency programs were established at both of Kentucky's medical schools. In 1972 a family practice residency program became operational at the University of Louisville. A study was conducted to determine the effectiveness of this program. We were especially interested in those factors that were associated with a physician's choice to practice in rural or urban medically underserved areas. The records of the 100 program graduates were reviewed to determine the physician's gender, ethnic background, hometown, and current practice location. A questionnaire was mailed to program graduates to obtain additional information about factors that influence physician practice location. For the purpose of this study, "rural" was defined as a community of less than 25,000. Sixty-eight of the program's 100 graduates currently practice in Kentucky. Forty-nine graduates serve patients in rural or medically underserved urban areas, and of those, 31 are located in Kentucky. Whites and those from rural hometowns were more likely to practice in rural communities than minorities or those from urban hometowns. However, minorities were more likely than whites to practice in medically underserved urban areas. No association was found between gender and practice location. Initial interest in rural practice and participation in financial aid programs requiring service in a rural area were associated with rural practice location, but participation in rural rotations at the predoctoral or residency training level were not. We conclude that the family practice training program at the University of Louisville has been successful in training generalist physicians to serve rural and medically underserved urban populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and expression of Drosophila HP1 homologs from a mealybug, Planococcus citri

The mealybug chromosome cycle is one of the most dramatic examples of genomic imprinting known. In embryos that are to become male the entire paternal chromosome set becomes heterochromatic and inactive at the blastoderm stage, while the maternal set remains active and euchromatic. HP1 is a protein from Drosophila melanogaster, which binds preferentially to heterochromatin on polytene chromosomes and is likely to be a modifier of position effect variegation. This paper describes the isolation and sequencing of two cDNA clones encoding HP1 homologs from the mealybug, Planococcus citri. The protein product of the cDNA clone that was closer to HP1 in sequence was expressed as a fusion protein in Escherichia coli, and polyclonal rat antibodies were raised against it. Immunohistochemistry to mealybug squash preparations showed that this protein was a male-specific nuclear protein, but that it was not specifically associated with the heterochromatic set of chromosomes.

A sequence motif found in a Drosophila heterochromatin protein is conserved in animals and plants

Modifiers of position-effect-variegation in Drosophila encode proteins that are thought to modify chromatin, rendering it heritably changed in its expressibility. In an attempt to identify similar modifier genes in other species we have utilized a known sequence homology, termed chromo box, between a suppressor of position-effect-variegation, Heterochromatin protein 1 (HP1), and a repressor of homeotic genes, Polycomb (Pc). A PCR generated probe encompassing the HP1 chromo box was used to clone full-length murine cDNAs that contain conserved chromo box motifs. Sequence comparisons, in situ hybridization experiments, and RNA Northern blot analysis suggest that the murine and human sequences presented in this report are homologues of the Drosophila HP1 gene. Chromo box sequences can also be detected in other animal species, and in plants, predicting a strongly conserved structural role for the peptide encoded by this sequence. We propose that epigenetic (yet heritable) changes in gene expressibility, characteristic of chromosomal imprinting phenomena, can largely be explained by the action of such modifier genes. The evolutionary conservation of the chromo box motif now enables the isolation and study of putative modifier genes in those animal and plant species where chromosomal imprinting has been described.

Mutation in a heterochromatin-specific chromosomal protein is associated with suppression of position-effect variegation in Drosophila melanogaster

We report here that a point mutation in the gene which encodes the heterochromatin-specific nonhistone chromosomal protein HP-1 in Drosophila melanogaster is associated with dominant suppression of position-effect variegation. The mutation, a G-to-A transition at the first nucleotide of the last intron, causes missplicing of the HP-1 mRNA. This suggests that heterochromatin-specific proteins play a central role in the gene suppression associated with heterochromatic position effects.

Distribution patterns of HP1, a heterochromatin-associated nonhistone chromosomal protein of Drosophila

We have previously reported the identification of a nonhistone chromosomal protein (nhcp-19; now called HP1) preferentially associated with the heterochromatin of Drosophila melanogaster. A detailed study of the HP1 distribution pattern on polytene chromosomes by immunofluorescent staining, using monoclonal antibody C1A9, has been carried out. The results indicate that this protein is found within the centric beta-heterochromatin, in cytological regions 31, 41 and 80, and throughout polytene chromosome 4. Staining of telomeres is frequently observed, those of chromosome arms 2R and 3R and the X chromosome being the most conspicuous. Analysis of a fourth chromosome insertional translocation T(3;4)f/In(3L)P confirms an autonomous interaction with chromosome 4 material. Similarly, the beta-heterochromatin distal to light on chromosome arm 2L, moved to position 97D2 on chromosome arm 3R in the rearrangement ltx13, is prominently stained using the C1A9 antibody. Staining of intact salivary glands indicates that this rearranged segment of beta-heterochromatin is not associated with the polytene chromocenter, but provides an independent structural reference point. HP1 is not observed in the nuclei of the early syncytial embryo, but becomes concentrated in the nuclei at the syncytial blastoderm stage (ca. nuclear division cycle 10). This suggests that heterochromatin formation occurs at approximately the same stage at which nuclei first become transcriptionally competent. Thus, the C1A9 antibody may serve as a useful marker for both structural and functional studies of the Drosophila nucleus.

Specific codon usage pattern and its implications on the secondary structure of silk fibroin mRNA

We have identified two distinctive regions of the repetitive unit nucleotide sequence of fibroin mRNA of Bombyx mori. The codon usage for the major amino acids, glycine, alanine and serine is distinctly different in these two regions, indicating that it is determined by the fibroin mRNA or gene structure but not by the tRNA population. Comparative computer analyses of nucleotide substitutions in the unit sequence suggest that selection has operated on the codon usage to optimize the secondary structure characteristic of the fibroin mRNA.

Production of antibodies using proteins in gel bands

A number of methods for preparing proteins as antigens have been described (1). These include solubilization of protein samples in buffered solutions (2), solubilization of nitrocellulose filters to which proteins have been adsorbed (3), and emulsification of protein bands in polyacrylamide gels for direct injections (4-8). The latter technique can be used to immunize mice or rabbits for production of antisera or to immunize mice for production of monoclonal antibodies (9-11). This approach is particularly advantageous when protein purification by other means is not practical, as in the case of proteins insoluble without detergent. A further advantage of this method is an enhancement of the immune response, since polyacrylamide helps to retain the antigen in the animal and so acts as an adjuvant (7). The use of the protein directly in the gel band (without elution) is also helpful when only small amounts of protein are available. For instance, in this laboratory, we routinely immunize mice with 5-10 µg total protein using this method; we have not determined the lower limit of total protein that can be used to immunize rabbits.

Identification of a nonhistone chromosomal protein associated with heterochromatin in Drosophila melanogaster and its gene

Monoclonal antibodies were prepared against a fraction of nuclear proteins of Drosophila melanogaster identified as tightly binding to DNA. Four of these antibodies were directed against a 19-kilodalton nuclear protein; immunofluorescence staining of the polytene chromosomes localized the antigen to the alpha, beta, and intercalary heterochromatic regions. Screening of a lambda gt11 cDNA expression library with one of the monoclonal antibodies identified a recombinant DNA phage clone that produced a fusion protein immunologically similar to the heterochromatin-associated protein. Polyclonal sera directed against the bacterial lacZ fusion protein recognized the same nuclear protein on Western blots. A full-length cDNA clone was isolated from a lambda gt10 library, and its DNA sequence was obtained. Analysis of the open reading frame revealed an 18,101-dalton protein encoded by this cDNA. Two overlapping genomic DNA clones were isolated from a Charon 4 library of D. melanogaster with the cDNA clone, and a restriction map was obtained. In situ hybridization with these probes indicated that the gene maps to a single chromosome location at 29A on the 2L chromosome. This general strategy should be effective for cloning the genes and identifying the genetic loci of chromosomal proteins which cannot be readily assayed by other means.

Hormonal regulation and expression of vitellogenin multigene family

Yolk proteins are the most abundant egg proteins in oviparous animals. They are deposited during oocyte maturation for use after fertilization and are synthesized in the liver or fat body as a common precursor termed vitellogenin. Hybridization with cloned DNA complementary to vitellogenin messenger RNA has revealed a surprisingly high degree of evolutionary conservation of sequence of vitellogenin genes among insects, amphibians and birds. The synthesis of vitellogenin in vertebrates is directly under the control of oestrogen at the level of gene transcription. In the frog, Xenopus, vitellogenin genes occur as a multigene family, four of which are actively expressed and are grouped as A and B genes. This multiplicity offers a useful system for investigating the possible selective hormonal regulation of expression of individual members of multigene families. When X. laevis vitellogenin genes were activated by oestrogen in the liver of whole animals or in cultures of parenchymal cells, the two groups of expressed genes were not induced in an identical manner in cells from male and female animals. The activation of A and B groups of genes was non-coordinate in male hepatocytes and coordinate in female cells. Prior exposure of male hepatocytes to oestradiol in vivo or in culture caused the pattern of expression to shift to that in female cells. Since the X. laevis oocyte itself does not synthesize vitellogenin in response to oestrogen, an attempt was made to activate its dormant vitellogenin genes by transferring oestrogen-binding proteins from the liver. Preliminary results show that the microinjection into the oocyte of a preparation containing liver receptor-hormone complex led to the synthesis of vitellogenin by the oocyte. Extension of these experiments will not only enable a more precise analysis of the activation of the vitellogenin multigene family to be made but will also provide direct functional evidence for the role played by steroid hormone receptors in regulating gene expression.

rRNA cleavage as an index of ppp(A2'p)nA activity in interferon-treated encephalomyocarditis virus-infected cells

In cell-free systems, 2-5A [ppp(A2'p)nA, n = 2 to greater than or equal to 4] activates a latent endoribonuclease, the 2-5A-dependent RNase, which cleaves rRNA in intact ribosomes into discrete and characteristic products (D. H. Wreschner et al., Nucleic Acids Res. 9:1571-1581, 1981). Here we present Northern blots which have identified the 18S or 28S origins of the cleaved products from rRNA. In addition, identical 3' termini were observed for fragments of 18S rRNA from a HeLa cell-free system incubated with 2-5A and from interferon-treated, encephalomyocarditis virus-infected HeLa cells. The previous assumption of identity of such fragments was based only on comigration on electrophoresis in agarose gels. We conclude that appropriate patterns of cleavage found in RNA isolated from intact cells are an indicator of prior 2-5A-dependent RNase activity. The assay of rRNA cleavage is relatively convenient and unambiguous. Accordingly, in the search for situations in which the 2-5A system may be active, it provides a useful alternative to the direct assay of 2-5A.

Construction and partial characterization of a recombinant DNA probe for locust vitellogenin messenger RNA

Double-stranded DNA complementary to poly(A)-containing RNA from the fat body of adult female locusts, Locusta migratoria, was synthesized. Hybrid molecules containing this cDNA was constructed in the PstI site of the plasmid pAT 153 by the technique of dC . dG tailing and amplified in Escherichia coli K-12 strain HB 101. Ten colonies of bacteria were identified as carrying recombinant plasmids containing DNA complementary to locust vitellogenin mRNA by (a) 'Northern' blot hybridization analysis and (b) hybrid selection of vitellogenin mRNA and immunological detection of the products of translation of the mRNA. Of the ten recombinant plasmids, one, termed plasmid 4E, containing a cDNA insert of about 650 nucleotides, was characterized in greater detail and a partial restriction map obtained. Using this hybrid plasmid it was possible to derive a value for the average content of vitellogenin mRNA in the adult female locust fat body as 1.5 x 10(5) molecules/cell, and to establish that the haploid genome of L. migratoria contains only one or two genes coding for vitellogenin.

Affinity labelling and characterization of the ppp(A2'p)nA-dependent endoribonuclease from different mammalian sources

The ppp(A2'p)nA-dependent endoribonucleases from a number of different mammalian sources have been investigated. The enzyme from reticulocyte lysates shows optimal activity of 50-150 mM KCl and requires the presence of Mg2+. Whilst the enzyme is inactivated after passage of reticulocyte lysates through Sephadex columns in the absence of ATP, it retains full activity provided ATP is included in the column buffer. The activity of the partially purified nuclease was unaffected by the addition of reticulocyte RNase inhibitor, which, in contrast, effectively inhibited other endogenous endonucleases. The ppp(A2'p)nA-dependent Rnase co-purified with a ppp(A2'p)nA-binding protein and with a protein which could be specifically covalently labelled with an oxidised radioactive analogue of ppp(A2'p)nA. This covalent labelling could be carried out either with the partially purified RNase or in crude extracts from rabbit reticulocytes, mouse Krebs and Ehrlich ascites tumour cells and human lymphoblastoid (Daudi) or HeLa cells. In each case the affinity labelled protein migrated to a position corresponding to a apparent molecular weight of about 85 000 on electrophoresis on dodecylsulphate/polyacrylamide gels. In all cases labelling could be prevented by the addition of an excess of unlabelled ppp(A2'p)nA but not, for example, by a similar excess of the biologically inactive dimer ppp(A2'p)'A. It is concluded that the RNase and ppp(A2'p)nA binding activities are likely to reside in the same molecule.

Evolutionary conservation of vitellogenin genes

Homologous and heterologous hybridizations in solution were performed between sheared genomic DNA and DNA complementary to vitellogenin mRNA of Xenopus, chicken, and migratory locust. The kinetics of hybridization and the thermal stability of the hybrids formed suggested a high degree of conservation of coding sequences of insect, amphibian, and avian vitellogenin genes. These cDNA probes hybridized to calf thymus DNA to a slight, but significant, extent, and not at all to Micrococcus lysodektikus DNA. DNA complementary to Xenopus albumin mRNA did not cross-hybridize significantly with locust or chicken DNA. Further evidence for the evolutionary conservation of vitellogenin genes was obtained from Southern blot analysis of restriction endonuclease-digested genomic DNA from a variety of vertebrate and invertebrate oviparous animals (Xenopus, chicken, migratory and desert locusts, yellow meal worm, carab moth, and Mediterranean fruitfly). When probed with cloned vitellogenin cDNAs from Xenopus and migratory locust, the DNA of these organisms showed varying degrees of homology of parts of the vitellogenin coding sequences. Southern blot analysis also showed that a part of the sequence specified in the cloned Xenopus vitellogenin cDNA was represented as repetitive DNA in the locust genome. However, cloned locust vitellogenin cDNA hybridized to discrete fragments of the restricted vertebrate DNA. These studies demonstrate a remarkably high degree of conservation of insect, amphibian, and avian vitellogenin genes.

Ribosomal RNA cleavage, nuclease activation and 2-5A(ppp(A2'p)nA) in interferon-treated cells

Ribosomal RNA (rRNA) in intact ribosomes is cleaved into discrete products on incubation of reticulocyte lysates or L-cell extracts with ppp(A2'p)3A. Cleavage of rRNA may, therefore, provide a useful assay for 2-5A (ppp)A2'p)nA; n = 2 to 4) or for the presence of a 2-5A-dependent nuclease. The results with reticulocyte lysates differed from those obtained in the L-cell-free system in that (a) a different RNA cleavage pattern was produced (with added L-cell ribosomes) and (b) cleavage was fully activated by the analogue ppp(A2'p)3A3'pCp. As might be expected from the relatively high levels of 2-5A present in interferon-treated, encephalomyocarditis virus (EMC)-infected L-cells, rRNA extracted from these cells was also cleaved. The cleavage pattern observed overlapped with that obtained on incubation of an L-cell-free system with 2-5A. Thus, not only is 2-5A present, but the 2-5A-dependent nuclease also appears to be active, in interferon-treated, EMC-infected L-cells.

The preparation and characterization of locust vitellogenin messenger RNA and the synthesis of its complementary DNA

Poly(A)+ (polyadenylated) RNA was isolated from vitellogenic female-locus fat-body by LiCl/urea extraction and poly(U)-Sepharose 4B affinity chromatography. Agarose-gel electrophoresis of this poly(A)+ RNA under denaturing conditions shows the presence of a high-molecular-weight species (greater than 31 S, 7100 nucleotides) as the major species, which is absent from the RNA prepared from male-locust fat-body. Inclusion of this poly(A)+ RNA in a mRNA-dependent reticulocyte-lysate system directs the synthesis of polypeptides that could be immunoprecipitated with monospecific antibodies against locust egg vitellin. DNA complementary (cDNA) to the poly(A)+ RNA was synthesized, and back-hybridization of the cDNA to its template reveals a major abundant species comprising about 45% of the total poly(A)+ RNA hybridizing with R0t 1/2 of 2 x 10(-2) mol . litre-1 . s. Abundant cDNA isolated from the total cDNA hybridizes to poly(A)+ RNA with a R0t 1/2 of 9 x 10(-3) mol . litre-1 . s. There are 9.1 x 10(3) copies of vitellogenin mRNA per cell of vitellogenic female-locust fat-body, comprising 55% of the poly(A)+ RNA and equivalent to 0.7% of total cellular RNA.

The Xenopus oocyte as a surrogate secretory system. The specificity of protein export

Combining messenger RNA from one kind of secretory cell with the cytoplasm of another such cell can reveal the nature and specificity of protein export mechanisms. We show that messenger RNAs from secretory cells of chickens, rats, mice, frogs, guinea-pigs, locusts and barley plants, when injected into Xenopus oocytes, direct the synthesis and export of proteins. Chicken ovalbumin, Xenopus albumin, mouse thyroid-stimulating hormone, locust vitellin and guinea-pig milk proteins were identified using specific antibodies, whilst chicken lysozyme and ovomucoid, rat albumin, Xenopus vitellogenin and rat seminal vesicle basic proteins were identified provisionally from their molecular weights. Certain endogenous proteins are sequestered and secreted although most oocyte proteins are not exported. Similarly the major polyoma viral protein and the simian virus 40 and polyoma tumour antigens are retained within the oocyte. Radioactive proteins exported by oocytes programmed with chicken oviduct or Xenopus liver RNA are not re-exported in detectable amounts when injected into fresh oocytes, nor is there secretion of chicken oviduct or guinea-pig mammary gland primary translation products prepared using wheat germ extracts. Thus the export of secretory proteins from oocytes cannot be explained by leakage and may require a cotranslational event. The secretory system of the oocyte is neither cell-type nor species-specific yet is highly selective. We suggest that the oocyte can be used as a general surrogate system for the study of gene expression, from transcription through translation to the final subcellular or extracellular destination of the processed protein.

Messenger RNA during early embryogenesis in Artemia salina: altered translatability and sequence complexity

RNA from developing embryos of Artemia salina (5, 10, and 20 h after re-initiation of development) was translated 3-10 times more efficiently in a rabbit reticulocyte lysate cell-free protein synthesizing system than RNA from dormant gastrulae. The latter did not appear to contain any significant amount of translation inhibitor activity. Ninety percent of the translatable activity in dormant gastrulae was recovered as poly(A)--RNA, whereas 80% of that in post-gastrular developing embryos was present as poly(A)+-RNA. The size of most polypeptides coded for by dormant gastrular RNA was less than 130,000 daltons whereas the size of those coded for by developing embryonic RNA was up to 200,000 daltons, which correlated with a corresponding shift to poly A-containing RNA of higher molecular weight. Two major polypeptides of about 37,000 daltons coded for by dormant gastrular RNA disappeared at 20 h after resumption of development. Hybridization of complementary DNA (cDNA) to a 1000-fold excess of the homologous poly(A)+-RNA revealed the presence of three complexity classes of mRNA. Forty-five percent, 30%, and 25% of RNA in dormant gastrulae were present as high, middle, and low abundance classes comprising about 10, 80, and 9700 species, respectively whereas in the nauplii there were 10, 150, and 7900 species of high, middle, and low abundancy sequences, respectively. Heterologous hybridizations using cDNA complementary to highly abundant messenger population of nauplii (isolated by chromatography on hydroxyapatite) to poly(A)+-RNA from dormant cysts showed considerably divergence in this class of messengers from the two developmental stages. Re-initiation of development of dormant Artemia gastrulae is thus characterized by a "re-programming" seen as a simultaneous and rapid increase in the polyadenylation and translatability of poly(A)+-RNA accompanied by a qualitative change in its sequence complexity.