Phleomycin resistance as a dominant selectable marker for plant cell transformation

An Alcaligenes strain emulates Bacillus thuringiensis producing a binary protein that kills corn rootworm through a mechanism similar to Cry34Ab1/Cry35Ab1

Crops expressing Bacillus thuringiensis (Bt)-derived insecticidal protein genes have been commercially available for over 15 years and are providing significant value to growers. However, there remains the need for alternative insecticidal actives due to emerging insect resistance to certain Bt proteins. A screen of bacterial strains led to the discovery of a two-component insecticidal protein named AfIP-1A/1B from an Alcaligenes faecalis strain. This protein shows selectivity against coleopteran insects including western corn rootworm (WCR). Transgenic maize plants expressing AfIP-1A/1B demonstrate strong protection from rootworm injury. Surprisingly, although little sequence similarity exists to known insecticidal proteins, efficacy tests using WCR populations resistant to two different Cry proteins show that AfIP-1A/1B and mCry3A differ in their mode of action while AfIP-1A/1B and the binary Cry34Ab1/Cry35Ab1 protein share a similar mode. These findings are supported by results of competitive binding assays and the similarity of the x-ray structure of AfIP-1A to Cry34Ab1. Our work indicates that insecticidal proteins obtained from a non-Bt bacterial source can be useful for developing genetically modified crops and can function similarly to familiar proteins from Bt.

Down-regulated Lotus japonicus GCR1 plants exhibit nodulation signalling pathways alteration

G Protein Coupled Receptor (GPCRs) are integral membrane proteins involved in various signalling pathways by perceiving many extracellular signals and transducing them to heterotrimeric G proteins, which further transduce these signals to intracellular downstream effectors. GCR1 is the only reliable plant candidate as a member of the GPCRs superfamily. In the legume/rhizobia symbiotic interaction, G proteins are involved in signalling pathways controlling different steps of the nodulation program. In order to investigate the putative hierarchic role played by GCR1 in these symbiotic pathways we identified and characterized the Lotus japonicus gene encoding the seven transmembrane GCR1 protein. The detailed molecular and topological analyses of LjGCR1 expression patterns that are presented suggest a possible involvement in the early steps of nodule organogenesis. Furthermore, phenotypic analyses of independent transgenic RNAi lines, showing a significant LjGCR1 expression down regulation, suggest an epistatic action in the control of molecular markers of nodulation pathways, although no macroscopic symbiotic phenotypes could be revealed.

Stable expression of antibiotic-resistant gene ble from Streptoalloteichus hindustanus in the mitochondria of Chlamydomonas reinhardtii

The mitochondrial expression of exogenous antibiotic resistance genes has not been demonstrated successfully to date, which has limited the development of antibiotic resistance genes as selectable markers for mitochondrial site-directed transformation in Chlamydomonas reinhardtii. In this work, the plasmid pBSLPNCB was constructed by inserting the gene ble of Streptoalloteichus hindustanus (Sh ble), encoding a small (14-kilodalton) protective protein into the site between TERMINVREP-Left repeats and the cob gene in a fragment of mitochondrial DNA (mtDNA) of C. reinhardtii. The fusion DNA-construct, which contained TERMINVREP-Left, Sh ble, cob, and partial nd4 sequence, were introduced into the mitochondria of the respiratory deficient dum-1 mutant CC-2654 of C. reinhardtii by biolistic particle delivery system. A large number of transformants were obtained after eight weeks in the dark. Subsequent subculture of the transformants on the selection TAP media containing 3 ìg/mL Zeomycin for 12 months resulted in genetically modified transgenic algae MT-Bs. Sequencing and Southern analyses on the mitochondrial genome of the different MT-B lines revealed that Sh ble gene had been integrated into the mitochondrial genome of C. reinhardtii. Both Western blot, using the anti-BLE monoclonal antibody, and Zeomycin tolerance analysis confirmed the presence of BLE protein in the transgenic algal cells. It indicates that the Sh ble gene can be stably expressed in the mitochondria of C. reinhardtii.

Yeast transformation to generate high-yielding clones

There are several ways to introduce non-native DNA into yeast cells, including chemical transformation and electroporation. Methods for both of these procedures are outlined in this chapter. Both methods permit the uptake of DNA from the environment through yeast cell membranes and this DNA can be episomally maintained or integrated into the host genome. However, yeast cells must first be made competent to permit passive entry of the DNA and various methods are outlined in this chapter to facilitate this. All of the described methods can be applied in combination with antibiotic or auxotrophic selection pressure.

Selectable genetic markers for nematode transgenesis

The nematode Caenorhabditis elegans has been used to study genetics and development since the mid-1970s. Over the years, the arsenal of techniques employed in this field has grown steadily in parallel with the number of researchers using this model. Since the introduction of C. elegans transgenesis, nearly 20 years ago, this system has been extensively used in areas such as rescue experiments, gene expression studies, and protein localization. The completion of the C. elegans genome sequence paved the way for genome-wide studies requiring higher throughput and improved scalability than provided by traditional genetic markers. The development of antibiotic selection systems for nematode transgenesis addresses these requirements and opens the possibility to apply transgenesis to investigate biological functions in other nematode species for which no genetic markers had been developed to date.

Evaluation and application of a luciferase fusion system for rapid in vivo analysis of RNAi targets and constructs in plants

The practical use of RNA-mediated approaches including antisense RNA, ribozymes and siRNAs for specific inhibition of gene expression is limited by lack of simple quantitative methods to rapidly test efficacy in vivo. There have been indications that cotransfer of target::reporter gene fusions with constructs designed against the target sequence, followed by quantification of transient reporter gene activity might be effective. Here, we report detailed testing of the approach in plants, using diverse target::luciferase fusions and antisense or ribozyme constructs. We used quantitative transient luciferase activity (Luc) assays to test antisense constructs against beta-glucuronidase, PR glucanase, vacuolar invertase and cucumber mosaic virus, as well as ribozymes against watermelon mosaic virus and tobacco anionic peroxidase. For constructs previously tested in transgenic plants, the results correspond well with those from the transient expression assay. Target susceptibility was generally not strongly influenced by luciferase fusion, and the assay was not highly dependent on target sequence length. Some sequences reduced Luc activity below the level for reliable quantification, but suitable alternative fusions were readily produced. Transcriptional and translation fusions were effective for 5' target::luc constructs. Translational fusions were more reliable for luc::target 3' constructs. With minimal preliminary work to prepare suitable target::luciferase fusions, the approach appears generally applicable for rapid in vivo validation of effectiveness and specificity of constructs designed for RNA-mediated down-regulation of plant genes.

Advances in selectable marker genes for plant transformation

Plant transformation systems for creating transgenics require separate process for introducing cloned DNA into living plant cells. Identification or selection of those cells that have integrated DNA into appropriate plant genome is a vital step to regenerate fully developed plants from the transformed cells. Selectable marker genes are pivotal for the development of plant transformation technologies because marker genes allow researchers to identify or isolate the cells that are expressing the cloned DNA, to monitor and select the transformed progeny. As only a very small portion of cells are transformed in most experiments, the chances of recovering transgenic lines without selection are usually low. Since the selectable marker gene is expected to function in a range of cell types it is usually constructed as a chimeric gene using regulatory sequences that ensure constitutive expression throughout the plant. Advent of recombinant DNA technology and progress in plant molecular biology had led to a desire to introduce several genes into single transgenic plant line, necessitating the development of various types of selectable markers. This review article describes the developments made in the recent past on plant transformation systems using different selection methods adding a note on their importance as marker genes in transgenic crop plants.

Secretory and continuous expression of Aspergillus niger glucose oxidase gene in Pichia pastoris

We proposed a yeast transformant cell incorporating the Aspergillus niger glucose oxidase gene (GOX gene), which is capable of constitutively as well as secretory expression. The GOX gene has been cloned in this study. This conclusion is based on the following: first, the ligated DNA determined by electrophoresis, was a 1489-1882bp fragment, close to the size of glucose oxidase (GOD), which is 1818bp. Secondly, the single open reading frame encoded a protein of 605 amino acids. Thirdly, secreted GOD recombinant proteins in the culture supernatants of the GOX gene transformant migrated as a single band in SDS-PAGE with an apparent molecular mass of between 75,000 and 100,000 Da, which is glycosylated GOD by the Pichia pastoris X-33 host machinery during the secretion process. Finally, the clones were cultured and secreted a protein, which possessed the GOD activity of catalyzing beta-d-glucose oxidation. With regard to the pH characteristics, the activity was more than 80% of the maximum activity in the range between pH 5 and pH 7. As for the temperature characteristics, the activity was not less than 92% of the maximum in the temperature range between 10 and 45 degrees C. The GOX gene transformant was able to maintain the GOD enzyme activity and produce recombinant GOD continuously for at least 2 weeks.

A Turnip yellow mosaic virus infection system in Arabidopsis suspension cell culture

Turnip yellow mosaic virus (TYMV) is a positive-strand RNA virus able to infect Arabidopsis thaliana. To establish a TYMV infection system in Arabidopsis cell culture, TYMV replicons with the capsid protein gene replaced by a reporter gene expressing the Sh ble protein conferring zeocin resistance were used to transfect Arabidopsis cells. Zeocin-resistant Arabidopsis calli were used to generate a suspension cell culture. Detection of viral proteins and RNAs after 18 months in culture demonstrated persistent replication of the replicon. The Arabidopsis cell culture yielded soluble, active replication complexes, providing a useful tool to study host factors involved in TYMV replication.

The tallysomycin biosynthetic gene cluster from Streptoalloteichus hindustanus E465-94 ATCC 31158 unveiling new insights into the biosynthesis of the bleomycin family of antitumor antibiotics

The tallysomycins (TLMs) belong to the bleomycin (BLM) family of antitumor antibiotics. The BLM biosynthetic gene cluster has been cloned and characterized previously from Streptomyces verticillus ATCC 15003, but engineering BLM biosynthesis for novel analogs has been hampered by the lack of a genetic system for S. verticillus. We now report the cloning and sequencing of the TLM biosynthetic gene cluster from Streptoalloteichus hindustanus E465-94 ATCC 31158 and the development of a genetic system for S. hindustanus, demonstrating the feasibility to manipulate TLM biosynthesis in S. hindustanus by gene inactivation and mutant complementation. Sequence analysis of the cloned 80.2 kb region revealed 40 open reading frames (ORFs), 30 of which were assigned to the TLM biosynthetic gene cluster. The TLM gene cluster consists of nonribosomal peptide synthetase (NRPS) genes encoding nine NRPS modules, a polyketide synthase (PKS) gene encoding one PKS module, genes encoding seven enzymes for deoxysugar biosynthesis and attachment, as well as genes encoding other biosynthesis, resistance, and regulatory proteins. The involvement of the cloned gene cluster in TLM biosynthesis was confirmed by inactivating the tlmE glycosyltransferase gene to generate a TLM non-producing mutant and by restoring TLM production to the DeltatlmE::ermE mutant strain upon expressing a functional copy of tlmE. The TLM gene cluster is highly homologous to the BLM cluster, with 25 of the 30 ORFs identified within the two clusters exhibiting striking similarities. The structural similarities and differences between TLM and BLM were reflected remarkably well by the genes and their organization in their respective biosynthetic gene clusters.

Selectable marker genes in transgenic plants: applications, alternatives and biosafety

Approximately fifty marker genes used for transgenic and transplastomic plant research or crop development have been assessed for efficiency, biosafety, scientific applications and commercialization. Selectable marker genes can be divided into several categories depending on whether they confer positive or negative selection and whether selection is conditional or non-conditional on the presence of external substrates. Positive selectable marker genes are defined as those that promote the growth of transformed tissue whereas negative selectable marker genes result in the death of the transformed tissue. The positive selectable marker genes that are conditional on the use of toxic agents, such as antibiotics, herbicides or drugs were the first to be developed and exploited. More recent developments include positive selectable marker genes that are conditional on non-toxic agents that may be substrates for growth or that induce growth and differentiation of the transformed tissues. Newer strategies include positive selectable marker genes which are not conditional on external substrates but which alter the physiological processes that govern plant development. A valuable companion to the selectable marker genes are the reporter genes, which do not provide a cell with a selective advantage, but which can be used to monitor transgenic events and manually separate transgenic material from non-transformed material. They fall into two categories depending on whether they are conditional or non-conditional on the presence of external substrates. Some reporter genes can be adapted to function as selectable marker genes through the development of novel substrates. Despite the large number of marker genes that exist for plants, only a few marker genes are used for most plant research and crop development. As the production of transgenic plants is labor intensive, expensive and difficult for most species, practical issues govern the choice of selectable marker genes that are used. Many of the genes have specific limitations or have not been sufficiently tested to merit their widespread use. For research, a variety of selection systems are essential as no single selectable marker gene was found to be sufficient for all circumstances. Although, no adverse biosafety effects have been reported for the marker genes that have been adopted for widespread use, biosafety concerns should help direct which markers will be chosen for future crop development. Common sense dictates that marker genes conferring resistance to significant therapeutic antibiotics should not be used. An area of research that is growing rapidly but is still in its infancy is the development of strategies for eliminating selectable marker genes to generate marker-free plants. Among the several technologies described, two have emerged with significant potential. The simplest is the co-transformation of genes of interest with selectable marker genes followed by the segregation of the separate genes through conventional genetics. The more complicated strategy is the use of site-specific recombinases, under the control of inducible promoters, to excise the marker genes and excision machinery from the transgenic plant after selection has been achieved. In this review each of the genes and processes will be examined to assess the alternatives that exist for producing transgenic plants.

Development of a novel recombinant adenovirus containing gfp–zeocin fusion expression cassette for conditional replication in p53-deficient human tumor cells

Two obstacles limiting the efficacy of nearly all cancer gene therapy trails are low gene transduction efficiency and the lack of tumor specificity. Fortunately, a replication-competent, E1B-deficient adenovirus (dl1520) was developed that could overcome these limitations, because it was capable of efficiently and selectively destroying tumor cells lacking functional p53. In an attempt to appraise the efficiency and safety of this approach, a novel recombinant adenovirus, r3/Ad, containing a gfp-zeocin expression cassette was constructed in this work. The study in vitro demonstrated that r3/Ad has the ability to replicate in and lyse only the p53-deficient human tumor cells such as the human glioblastoma cells (U251) and human bladder cells (EJ) but not in the human fibroblast cells (MRC-5) with functional p53. Importantly, this gfp-zeocin fusion gene driven by the bipromoter (CMV and EM-7) could be used as an effective selective marker and reporter in prokaryotic and eukaryotic cells; and also zeocin as a selective marker could minimize contamination of the recombinant virus by the wt-Ad5. Additionally, it was found that the r3/Ad could be useful for studying the selective replication of E1B-deficient adenovirus in vivo, it could be used as a "guide" to study the ability of the recombinant adenovirus to spread and to infect distant tumor cells in any tumor bearing animal model by GFP as a reporter. This may help determine the safety of using any E1B-deficient adenovirus in cancer gene therapy.

Development of a reporter system for the yeast Schwanniomyces occidentalis: influence of DNA composition and codon usage

In this paper we report on searching for suitable reporters to monitor gene expression and protein secretion in the amylolytic yeast Schwanniomyces occidentalis. Several potential reporter and marker genes, formerly shown to be functional in other yeasts, were cloned downstream from the homologous invertase gene (INV) promoter and their activity was followed in conditions of repression and derepression of the INV promoter. However, neither beta-glucuronidase nor beta-lactamase nor phleomycin resistance-conferring gene, all originating from E. coli, were expressed in S. occidentalis cells to such a level to allow for monitoring of their activity. All the reporter genes tested have a higher percentage of GC (47-62%) in their DNA compared to the DNA composition of S. occidentalis genes that are more AT-rich (36% GC). The codon usage of all the reporter genes also varies from that of 16 so far sequenced S. occidentalis genes. This suggests that an appropriate composition of DNA and a codon usage similar to S. occidentalis genes might be very important parameters for an efficient expression of a heterologous gene in Schwanniomyces occidentalis. Indeed, two genes originating from Staphylococcus aureus, with an AT-content in their DNA similar to that of S. occidentalis, were functionally expressed in S. occidentalis cells. Both a phleomycin resistance-conferring gene and a chloramphenicol acetyltransferase-encoding gene thus represent suitable reporters of gene expression and protein secretion in S. occidentalis. Additionally, we show in this work that the transcription-regulating region and the signal peptide sequence of the S. occidentalis invertase gene were efficient to direct gene expression and subsequent protein secretion in Saccharomyces cerevisiae.

A new transformation-regeneration procedure in the model legume Lotus japonicus: root explants as a source of large numbers of cells susceptible to Agrobacterium-mediated transformation

We describe herein a simple and efficient transformation procedure for the production of transgenic Lotus japonicus plants. In this new procedure, dedifferentiated root explants, used as starting material, are the source of a large number of cells that are competent for the regeneration procedure, with a high susceptibility to Agrobacterium infection. The application of this protocol resulted in a tenfold increase in the number of transformants produced by a single plant in comparison to the widely used hypocotyl transformation procedure. Furthermore, our procedure allowed the use of intact plants stored for a long time at 4 degrees C, thus providing a potential continuous supply of explants for transformation experiments. The overall time of incubation under tissue culture conditions required to obtain a plant transferable into soil is 4 months. The transgenic nature of the transformants was demonstrated by the detection of beta-glucuronidase (GUS) activity in the primary transformants and by molecular analysis. Stable transformation was indicated by Mendelian segregation of the hygromycin selectable marker and of the gusA activity after selfing of the transgenic plants.

Positive-negative selection for homologous recombination in Arabidopsis

In plants gene knock-outs and targeted mutational analyses are hampered by the inefficiency of homologous recombination. We have developed a strategy to enrich for rare events of homologous recombination in Arabidopsis using combined positive and negative selection. The T-DNA targeting construct contained two flanking regions of the target alcohol dehydrogenase gene as homologous sequences, and neomycin phosphotransferase and cytosine deaminase as positive and negative markers, respectively. A root explant transformation procedure was used to obtain transgenic calli. Among 6250 transformants isolated by positive selection, 39 were found to be resistant to negative selection as well. Of these 39, at least one had undergone homologous recombination correlated with a unidirectional transfer of information. Although the ADH locus was not changed, our data demonstrate that a homologous recombination event can be selected by positive negative selection in plants.

Utilization of the Streptoalloteichus hindustanus resistance determinant ShBle as a protein framework: effect of mutation upon ShBle dimerization and interaction of C-terminal displayed peptide epitopes

We have selected the Streptoalloteichus hindustanus bleomycin-resistance protein ShBle, a 28-kDa homodimer, as a scaffold for the display of bioactive peptides and other peptide epitopes. To create a monomeric scaffold, we investigated the effect of mutating residue proline 9 to glycine. This residue plays a critical role in ShBle dimerization by affecting the position of the eight N-terminal residues which secure the interaction between the monomeric subunits. We demonstrate that this mutation weakens the dimerization interaction, resulting in establishment of a stable equilibrium between monomeric and dimeric ShBle species in solution. Circular dichroism and SDS-PAGE data indicate that the Pro9Gly mutation does not disrupt the structure of the molecule. Production of a fully monomeric form of ShBle required complete removal of the eight-residue N-terminal peptide, and the interaction across the now solvent-exposed hydrophobic interface of the ShBle monomer was insufficient to drive dimerization. To demonstrate efficient display of epitope tags on the ShBle protein, we displayed dual-octapeptide FLAG tags at the protein C-terminus. These additions did not interfere with protein folding or activity. The resulting ShBle scaffold was used to compare the efficiency of two commercial FLAG-specific antibodies by biosensor.

Baculovirus immediate-early promoter-mediated expression of the Zeocin resistance gene for use as a dominant selectable marker in dipteran and lepidopteran insect cell lines

The antibiotic Zeocin, a derivative of phleomycin, was evaluated for use as a selection system in both dipteran and lepidopteran insect cell lines. Growth of Drosophila cell lines, Kc1 and SL2, was inhibited at Zeocin concentrations of 50 and 75 microg/ml, respectively, while the Spodoptera cell line, Sf9, was inhibited at a concentration of 250 microg/ml Zeocin. The mammalian cytomegalovirus (CMV) and Simian virus 40 (SV40) early promoters did not function in these insect cell lines. Several baculovirus-derived immediate-early (IE) promoters from the Orgyia pseudotsugata multicapsid nucleopolyhedrovirus (OpMNPV) and Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) were used to drive expression of the Zeocin resistance gene (ble) in these cell lines. The resulting plasmid vectors enabled selection of Zeocin-resistant cell lines within 3-4 weeks. Gene amplification events in the presence of increasing Zeocin concentrations were not detected using Southern blot analysis. Furthermore, the function of the baculovirus IE promoters, as demonstrated by beta-galactosidase expression, was not detectable in a variety of mammalian cell lines tested. A cloning/shuttle vector, containing ten unique restriction sites, was constructed which allows for selection of Zeocin resistance in insect cell lines and in Escherichia coli.

A promoter identified in the 3' end of the Ac transposon can be activated by cis-acting elements in transgenic Arabidopsis lines

In experiments directed to develop a promoter trap strategy in Arabidopsis, using a Ds chimaeric element containing a promoterless beta-glucuronidase (GUS) gene, we identified a promoter in the 3' end region of the Ac transposable element. The promoter initiates most of the transcripts at coordinate 4250 in the Ac sequence and is oriented towards the internal part of the element. When fused to a promoterless GUS gene, the promoter allows transient expression in Arabidopsis leaves. After stable integration into the Arabidpsis genome, no GUS activity was observed in most of the transformed lines analysed. Only two of them exhibited different tissue-specific GUS expression. When a CaMV 35S promoter was introduced into the transformation vector, downstream to the reporter gene, a high level of GUS activity was observed in all the transformants. These results strongly suggest that the promoter is not normally expressed at a significant level in Arabidopsis transformed lines except when activated by neighbouring cis-acting enhancer elements. This opens an interesting possibility for using this promoter to develop 'enhancer trap' strategies in Arabidopsis. Since only one Ac transcript, initiating in the 5' end region of the element has been reported to date in maize, the putative biological function of the promoter remains an open question.

Arabidopsis mutants deficient in T-DNA integration

Arabidopsis thaliana mutants originally isolated as hypersensitive to irradiation were screened for the ability to be transformed by Agrobacterium transferred DNA (T-DNA). One of four UV-hypersensitive mutants and one of two gamma-hypersensitive mutants tested showed a significant reduction in the frequency of stable transformants compared with radioresistant controls. In a transient assay for T-DNA transfer independent of genomic integration, both mutant lines took up and expressed T-DNA as efficiently as parental lines. These lines are therefore deficient specifically in stable T-DNA integration and thus provide direct evidence for the role of a plant function in that process. As radiation hypersensitivity suggests a deficiency in repair of DNA damage, that plant function may be one that is also involved in DNA repair, possibly, from other evidence, in repair of double-strand DNA breaks.

Activity of the yeast FLP recombinase in Arabidopsis

The coding sequence for FLP recombinase, originally from the 2 mu plasmid of Saccharomyces cerevisiae, was introduced into Arabidopsis behind the cauliflower mosaic virus 35S promoter. FLP activity was monitored by the glucuronidase activity resulting from inversion of an antisense-oriented GUS reporter gene flanked by a pair of FRT target sites in inverted repeat. FLP-dependent Gus activity was observed in both transient assays and transgenic plants. The FLP system will be useful for a variety of in planta genetic manipulations.

A selectable bifunctional beta-galactosidase::phleomycin-resistance fusion protein as a potential marker for eukaryotic cells

The Sh ble gene, conferring phleomycin resistance (PhR), was fused in frame to both the 3' and 5' ends of the Escherichia coli lacZ gene. The bifunctionality of the resulting 130-kDa hybrid proteins was demonstrated in E. coli and in the fungus, Tolypocladium geodes. PhR transformants of both organisms could be selected for. All transformants from E. coli and most from T. geodes displayed beta Gal activity. In the fungal host, higher transformation frequencies and greater levels of beta Gal activity were observed in clones harboring the lacZ::Sh ble fusion, as compared to the Sh ble::lacZ configuration. This system appears to be a potentially useful tool for the direct selection of transformants, and the evaluation of gene expression and regulation in a wide variety of prokaryotic and eukaryotic hosts.

High efficiency transformation of Tolypocladium geodes conidiospores to phleomycin resistance

A convenient and efficient transformation system has been developed for the filamentous fungus Tolypocladium geodes. In contrast to most of the commonly described techniques requiring prior preparation of protoplasts or spheroplasts, this method leads to high efficiency transformation of T. geodes conidiospores following moderate lytic enzyme treatment. Competent cells so obtained are still resistant to osmotic pressure and can be stored frozen without loss of viability. The highest transformation frequency (3-5 x 10(3) transformants per microgram of DNA) was obtained with plasmid pUT737 containing the Sh ble gene conferring phleomycin resistance under the control of a strong promoter isolated from Trichoderma reesei. Southern hybridization revealed multiple integration sites of plasmid DNA into the T. geodes nuclear DNA despite the absence of homology between the transforming DNA and the recipient genome. Instability could not be detected for the phleomycin phenotype during more than five generations of mitotic growth under non-selective conditions.

Cloning of Saccharomyces cerevisiae promoters using a probe vector based on phleomycin resistance

Vectors that confer high levels of phleomycin (Ph) resistance to Saccharomyces cerevisiae have been constructed with the TEF1 and ENO1 promoters, the Tn5 ble gene and the CYC1 terminator. They are able to transform yeast cells grown on rich glucose medium containing a moderate level of Ph (10 micrograms/ml, corresponding to 100-fold the minimal inhibitory concentration). Frequencies of transformation are identical to those obtained with the URA3 marker on a defined medium. A promoter probe vector, based on the same ble marker, enabled us to isolate sequences from chromosomal yeast DNA that had promoter activities. These DNA fragments have been sequenced and those which promote the highest levels of Ph resistance have been found to be either A + T-rich or have a potentially new and more efficient translation start site.