Synthesis and secretion of human nerve growth factor by Saccharomyces cerevisiae

EasyCloneMulti: A Set of Vectors for Simultaneous and Multiple Genomic Integrations in Saccharomyces cerevisiae

Saccharomyces cerevisiae is widely used in the biotechnology industry for production of ethanol, recombinant proteins, food ingredients and other chemicals. In order to generate highly producing and stable strains, genome integration of genes encoding metabolic pathway enzymes is the preferred option. However, integration of pathway genes in single or few copies, especially those encoding rate-controlling steps, is often not sufficient to sustain high metabolic fluxes. By exploiting the sequence diversity in the long terminal repeats (LTR) of Ty retrotransposons, we developed a new set of integrative vectors, EasyCloneMulti, that enables multiple and simultaneous integration of genes in S. cerevisiae. By creating vector backbones that combine consensus sequences that aim at targeting subsets of Ty sequences and a quickly degrading selective marker, integrations at multiple genomic loci and a range of expression levels were obtained, as assessed with the green fluorescent protein (GFP) reporter system. The EasyCloneMulti vector set was applied to balance the expression of the rate-controlling step in the β-alanine pathway for biosynthesis of 3-hydroxypropionic acid (3HP). The best 3HP producing clone, with 5.45 g.L^-1 of 3HP, produced 11 times more 3HP than the lowest producing clone, which demonstrates the capability of EasyCloneMulti vectors to impact metabolic pathway enzyme activity.

New therapeutic approaches in the treatment of diabetic keratopathy: a review

The cornea is densely innervated, and the integrity of these nerve fibres is critical in maintaining the refractive and protective functions of the cornea. Many ocular and systemic diseases can adversely affect corneal sensory nerves and consequently impair their function, with vision loss being the inevitable consequence of severe corneal neurotrophic ulceration. However, current standard treatments regimens are often ineffective. Over the past three decades, the role of growth factors in maintaining the normal structure and function of the cornea, and in corneal epithelial healing, has become increasingly evident. Many preclinical and clinical trials have shown that growth factors and cytokines can significantly enhance epithelialization (epithelial proliferation and migration) and consequently accelerate wound healing. More recently, local/topical administration of insulin, naltrexone (opioid antagonist) and nicergoline (ergoline derivatives) were found to improve, and significantly increase, the corneal wound healing rate. This report reviews the major attributes of these growth factors and therapeutic agents that may be used in ameliorating impaired corneal wound healing, and presents a perspective on the potential clinical use of these agents as a new generation of ophthalmic pharmaceuticals for the treatment of diabetic keratopathy.

Halophilic beta-lactamase as a new solubility- and folding-enhancing tag protein: production of native human interleukin 1alpha and human neutrophil alpha-defensin

The amino acid composition of halophilic enzymes is characterized by an abundant content of acidic amino acid, which confers to the halophilic enzymes extensive negative charges at neutral pH and high aqueous solubility. This negative charge prevents protein aggregation when denatured and thereby leads to highly efficient protein refolding. Beta-lactamase from periplasmic space of moderate halophile (BLA), a typical halophilic enzyme, can be readily expressed as a native, active form in Escherichia coli cytoplasm. Similar to other halophilic enzymes, BLA is soluble upon denaturation by heat or urea treatments and, hence, can be efficiently refolded. Such high solubility and refolding efficiency make BLA a potential fusion partner for expression of aggregation-prone heterologous proteins to be expressed in E. coli. Here, we succeeded in the soluble expression of several "difficult-to-express" proteins as a BLA fusion protein and verified biological activities of human interleukin 1alpha and human neutrophil alpha-defensin, HNP-1.

Recombinant human nerve growth factor with a marked activity in vitro and in vivo

Recombinant human nerve growth factor (rhNGF) is regarded as the most promising therapy for neurodegeneration of the central and peripheral nervous systems as well as for several other pathological conditions involving the immune system. However, rhNGF is not commercially available as a drug. In this work, we provide data about the production on a laboratory scale of large amounts of a rhNGF that was shown to possess in vivo biochemical, morphological, and pharmacological effects that are comparable with the murine NGF (mNGF), with no apparent side effects, such as allodynia. Our rhNGF was produced by using conventional recombinant DNA technologies combined with a biotechnological approach for high-density culture of mammalian cells, which yielded a production of approximately 21.5 +/- 2.9 mg/liter recombinant protein. The rhNGF-producing cells were thoroughly characterized, and the purified rhNGF was shown to possess a specific activity comparable with that of the 2.5S mNGF by means of biochemical, immunological, and morphological in vitro studies. This work describes the production on a laboratory scale of high levels of a rhNGF with in vitro and, more important, in vivo biological activity equivalent to the native murine protein.

Efficient expression, purification and characterization of mouse salivary alpha-amylase secreted from methylotrophic yeast, Pichia pastoris

We constructed a secretion vector of mouse salivary alpha-amylase, pPAM, using the AOX1 promoter-terminator and the secretion signal of 128 kDa pGKL killer protein, for an alternative yeast, Pichia pastoris. Taking advantage of multicopy insertion of the expression cassette and optimized growth conditions, we succeeded in highly efficient extracellular production (approximately 240 microg/ml) of mouse alpha-amylase in the 10 ml scale by conventional flask culture: this efficiency was about 90-fold higher than that of Saccharomyces cerevisiae. Growth temperature of cells was critical for efficient production of alpha-amylase. P. pastoris transformants secreted both core-glycosylated and non-glycosylated alpha-amylase molecules with a glycosylated:non-glycosylated ratio of about 20:80. Both glycosylated and non-glycosylated alpha-amylases were purified separately to apparent homogeneity. The signal sequence was correctly processed in both species, and the molecular masses of glycosylated and non-glycosylated alpha-amylase were determined to be 58 600 and 56 300, respectively, by mass spectrometry. We further studied the outer chain glycosylation of engineered mouse alpha-amylase secreted by P. pastoris.

Secretion of mouse alpha-amylase from Kluyveromyces lactis

We constructed two mouse alpha-amylase secretion vectors for Kluyveromyces lactis using the well-characterized signal sequence of the pGKL 128 kDa killer precursor protein. Both PHO5 and PGK expression cassettes from Saccharomyces cerevisiae directed the expression of mouse alpha-amylase in YPD medium at a similar level of efficiency. K. lactis transformants secreted glycosylated and non-glycosylated alpha-amylase into the culture medium and both species were enzymatically active. The K. lactis/S. cerevisiae shuttle secretion vector pMI6 was constructed, and K. lactis MD2/1(pMI6) secreted about four-fold more alpha-amylase than S. cerevisiae YNN27 harboring the same plasmid, indicating that K. lactis is an efficient host cell for the secretion and production of recombinant proteins.

Transport and elimination of recombinant human NGF during long-term delivery to the brain

The gene for human nerve growth factor (NGF) has been cloned into a mammalian cell line and large quantities of recombinant human NGF (rhNGF) can now be produced for clinical use, but little is known about the fate of rhNGF following delivery to the brain. In this study, we implanted polymer matrices containing 125I-labeled rhNGF into the brains of adult rats and measured spatial distributions of the released protein for 8 weeks after implantation. NGF content in the tissue was determined by counting gamma radiation in thick (1 mm) sections and by autoradiography of thin (20 microns) sections. For the first several days, the rate of NGF release from the polymer matrix was high (approximately 100 ng/day); maximal NGF concentrations, measured at the polymer-tissue interface, were correspondingly high (> 20 micrograms/ml) though day 4. At later times, the release rate decreased (2-10 ng/day) and lower maximal concentrations were observed (1-10 micrograms/ml). NGF levels were always highest in the tissue sections closest to the polymer; during the 8 weeks of the experiment, NGF levels measured in thick sections decreased 100-fold, from 30 ng/section at day 2 to 0.3 ng/section at day 54. The first 10-fold decrease occurred during the first 10 days of the study; a further 6 weeks was required to achieve the second 10-fold decrease. Throughout the experiment, the majority of NGF remained within a restricted zone around the polymer at all times; the mass of NGF decreased to 10% of the maximal level within 2-3 mm of the polymer matrix. At early times (< 1 week), radiolabel corresponding to > 20 pg of NGF was also detected in regions of the brain further removed from the polymer. Comparison of local rhNGF concentration profiles with a simple mathematical model indicated that rhNGF diffuses through the brain interstitial space and is eliminated with a half-life of approximately 45 min, although elimination appears to be substantially slower in white matter regions. This limited ability of NGF to penetrate and be retained within the brain tissue indicates that NGF will need to be delivered almost directly to the target tissue for efficacy.

Secretion of active human lysozyme by Acremonium chrysogenum using a Fusarium alkaline protease promoter system

We constructed expression vectors for Acremonium chrysogenum using a Fusarium alkaline protease promoter region and tested their potential as secretion systems for foreign proteins using the human (h)-lysozyme gene as an indicator. The gene encoding h-lysozyme was linked to the coding region of (1) the carboxy terminal of the alkaline protease pre peptide, (2) the carboxy terminal of the prepro peptide, (3) three amino acids of the mature protein preceded by the prepro peptide and (4) the carboxy terminal of chicken lysozyme signal peptide, inserted into the genomic DNAs of A. chrysogenum and expressed under the control of the alkaline protease promoter. The transformants of A. chrysogenum with each of these plasmids secreted enzymatically active h-lysozyme. A maximum yield in excess of 40 mg l-1 was obtained when h-lysozyme was linked to the carboxy terminal of alkaline protease prepro peptide. The majority of the amino terminal sequence of the purified h-lysozyme from the culture supernatant was identical with that of authentic h-lysozyme, but it showed some heterogeneity.

Functional analysis of the threonine- and serine-rich Gp-I domain of glucoamylase I from Aspergillus awamori var. kawachi

Glucoamylase I (GAI) from Aspergillus awamori var. kawachi hydrolyzes raw starch efficiently and is composed of three functional domains: the amino-terminal catalytic GAI' domain (A-1 to V-469), the threonine- and serine-rich O-glycosylated Gp-I domain (A-470 to V-514), and the carboxy-terminal raw starch-binding Cp domain (A-515 to R-615). In order to investigate the role of the Gp-I domain, an additional repeat of Gp-I and internal deletions of the entire Gp-I sequence or parts of the Gp-I sequence were introduced within Gp-I. All mutant genes as well as the wild-type gene were inserted into a yeast-secretion vector, YEUp3H alpha, and expressed in Saccharomyces cerevisiae. Wild-type GAI expressed in yeast cells (GAY), GAGpI, having an extra Gp-I, and GA delta 470-493, lacking the A-470-to-T-493 sequences of Gp-I, were successfully secreted into the culture medium. On the other hand, GA delta 470-507, lacking A-470 to S-507, and GA delta GpI, lacking the entire Gp-I (A-470-to-V-514) sequence, failed to be secreted and remained in the yeast cells. The carbohydrate content of GAGpI was 1.2 times higher than that of GAY and 2.4 times higher than that of the original GAI. The raw starch digestibility of GAGpI was almost the same as that of GAY but was 1.5 times faster than that of GAI.(ABSTRACT TRUNCATED AT 250 WORDS)

Production and characterization of recombinant mouse brain-derived neurotrophic factor and rat neurotrophin-3 expressed in insect cells

Bioactive brain-derived neurotrophic factor (BDNF) and neurotrophin-3 were produced using the baculovirus expression system and purified to homogeneity using ion-exchange and reversed-phase chromatography. Yields of purified neurotrophin-3 (300-500 micrograms/L) were similar to levels reported for baculovirus-expressed nerve growth factor (NGF), whereas initial yields of BDNF were significantly lower (20-50 micrograms/L). Improved production of BDNF (150-200 micrograms/L) was achieved by expressing BDNF from a chimeric prepro-NGF/mature BDNF construct using the Trichoplusia ni insect cell line. Tn-5B1-4. Examination of the distribution of BDNF protein from both the non-chimeric prepro-BDNF and the chimeric prepro-NGF/mature BDNF viruses in Sf-21- and Tn-5B1-4-infected cells suggests a specific deficiency in the Tn-5B1-4 cells in processing the nonchimeric precursor. In addition, the vast majority of the BDNF protein at 2 days after infection was intracellular and insoluble. N-terminal amino acid sequencing of purified recombinant BDNF and neurotrophin-3 demonstrated that the insect cells processed their precursors to the correct N-terminus expected for the mature protein. Bioactivity was characterized in vitro on primary neuronal cultures from the CNS and PNS.

Protective effect of nerve growth factor against glutamate-induced neurotoxicity in cultured cortical neurons

The effect of recombinant human nerve growth factor (hNGF) and mouse NGF on cultured rat cortical neurons was examined. The DNA fragment coding the human NGF gene was isolated and inserted downstream from the SV40 promoter in a plasmid containing the dihydrofolate reductase cDNA, and this plasmid was introduced into Chinese hamster ovary (CHO) cells to establish cells producing recombinant hNGF. The recombinant hNGF protein secreted by CHO cells was confirmed to be biologically active in an assay using PC12 cells. Brief exposure of cortical cells to glutamate followed by incubation with glutamate-free medium reduced cell viability by 60-70% when compared with the control culture. Simultaneous addition of recombinant hNGF or mouse NGF to rat cortical cultures with glutamate did not affect this reduction of cell viability. However, 24 h pretreatment of rat cortical cultures with recombinant hNGF or mouse NGF resulted in a significant reduction of glutamate-induced neuronal damage. Mouse NGF also protected cortical neurons against N-methyl-D-aspartate (NMDA)- and kainate-induced neuronal damage. These findings suggest that NGF can protect cortical neurons against glutamate-induced neurotoxicity.

Fed-batch culture of insect cells: a method to increase the yield of recombinant human nerve growth factor (rhNGF) in the baculovirus expression system

A fed-batch method was developed which increased the density of insect cells (Spodoptera frugiperda, Sf-9 cells) in suspension culture and the feeding of nutrients improved the yield of a recombinant protein produced by a baculovirus expression system. Analysis of spent medium samples indicated that depletions of glucose and glutamine correlated with the retardation of cell growth. Feeding of a mixture of nutrients consisting of glucose, glutamine, yeastolate and lipids solution restored the growth rate. In fed-batch culture, cell density was increased from 3 x 10(6) cells per ml to 1.2 x 10(7) cells per ml and the increased cell density enhanced the yield of the desired recombinant product, in this case, human nerve growth factor (rhNGF). The optimal conditions for the production of rhNGF were also defined by selecting the appropriate viral multiplicity of infection (MOI). At a cell density of 5 x 10(6) ml-1, a MOI of 0.05 (plaque forming units per cell) gave the highest yield of rhNGF in culture fluid 3 d post-infection. The yield of rhNGF was 20 mg l-1. The fed-batch method was scaled up to 12 l stirred bioreactor.

Biologically active human and mouse nerve growth factors secreted by the yeast Saccharomyces cerevisiae

Nerve growth factor (NGF) is a trophic agent that is essential for the development and survival of sympathetic and sensory nerves. A chemically-synthesized DNA fragment encoding human NGF (hNGF) and a cDNA encoding mouse NGF (mNGF) were engineered for expression in the yeast, Saccharomyces cerevisiae. Expression and secretion of hNGF and mNGF was attempted under the direction of the yeast PGK promoter and with various leader sequences. Among the leader sequences tested, that of the yeast alpha-factor successfully directed secretion of both hNGF and mNGF that were correctly processed. The content of the recombinant NGF (reNGF) in the culture supernatant was estimated to be 1 microgram/ml. The yeast-produced reNGF was able to bind to NGF receptors in rat pheochromocytoma (PC12) cells as efficiently as the standard mNGF, and partially purified reNGF could induce neurite outgrowth of PC12 cells. Thus, we have demonstrated that biologically active human and mouse reNGF can be produced in yeast cells.

Molecular analysis of POP2 gene, a gene required for glucose-derepression of gene expression in Saccharomyces cerevisiae

We have isolated a new mutant of Saccharomyces cerevisiae that exhibits a glucose-derepression resistant (and sucrose-non-fermentor) phenotype. This mutant was obtained by screening for overproduction of alpha-amylase in a strain containing the mouse alpha-amylase gene under the control of the PGK promoter. The mutation designated pop2 (PGK promoter directed over production). The pop2 mutant overproduced amylase 5-6 fold and displayed several other pleiotropic defects: (1) resistance to glucose derepression, (2) temperature-sensitive growth, (3) failure of homozygous diploid cells to sporulate and (4) reduced amount of reserve carbohydrates. We mapped pop2 to chromosome XIV, distal to lys9 and SUP28, indicating that POP2 is a newly-identified locus. We isolated the POP2 gene from two yeast strains of different genetic backgrounds, S288C and A364A, and determined their nucleotide sequences. The predicted amino acid sequence of the POP2 protein contains three glutamine-rich region, a proline-rich region and a serine/threonine-rich region, characteristic of many transcription factors. Steady state levels of RNA transcribed from the PGK-amylase fusion gene and from endogenous PGK gene in stationary-phase pop2 cells were 5- to 10-fold higher than those observed in wild-type cells, showing that the pop2 mutation affects transcription of the PGK gene transcription.

Biochemical characterization of recombinant human nerve growth factor

Recombinant human nerve growth factor (rhNGF) was expressed and secreted by Chinese hamster ovary cells and purified to homogeneity using ion-exchange and reversed-phase (RP) chromatography. The isolated product was shown to be consistent with a 120-amino-acid residue polypeptide chain by amino acid composition, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), RP-HPLC, and mass spectrometry and with an N-terminal sequence consistent with that expected from the cDNA for human nerve growth factor. By size-exclusion chromatography, rhNGF behaves like a noncovalent dimer. Limited enzymatic digests of the 120-residue monomer produced additional species of 118 (trypsin, removal of the C-terminal Arg119-Ala120 sequence) and 117 (trypsin plus carboxypeptidase B, removal of the C-terminal Arg118-Arg119-Ala120 sequence) residues. Each of these species was isolated by high-performance ion-exchange chromatography and characterized by amino acid and N-terminal sequence analyses, SDS-PAGE, RP-HPLC, and mass spectrometry. All three species were present in the digests as both homodimeric and heterodimeric combinations and found to be equipotent in both the chick dorsal root ganglion cell survival and rat pheochromocytoma neurite extension assays.

Production and characterization of recombinant mouse neurotrophin-3

Neurotrophin-3 (NT-3) is a neurotrophic-factor that has recently been cloned on the basis of its structural similarity to other members of the nerve growth factor (NGF) gene family. In order to produce this protein, a recombinant vaccinia virus containing the coding region for mouse NT-3 was constructed. Conditioned medium harvested from cells infected with the recombinant vaccinia virus contained biologically active NT-3 that was purified by chromatography on controlled-pore glass and reversed-phase and gel-filtration high-pressure liquid chromatography. Approximately 200 micrograms purified NT-3 was obtained from a single cell-factory flask (1.6 1 conditioned medium). N-terminal protein sequencing showed that the mature factor was processed from the precursor at the expected site and its amino acid composition agreed with that predicted from the DNA sequence. The biological activity of the recombinant protein was tested on dissociated neurons prepared from chick embryos. Using spinal sensory neurons, the concentration of purified recombinant NT-3 allowing half-maximal survival was determined to be 25 pg/ml.

Synthesis of the biologically active beta-subunit of human nerve growth factor in Escherichia coli

The gene (NGFB) encoding the beta subunit of mature human nerve growth factor (hNGFB) was subcloned into the pJLA503 expression vector under the control of bacteriophage promoters PR and PL, and expressed in Escherichia coli. The recombinant protein represented approximately 3% of the total cellular protein. Biologically active hNGFB was solubilized (0.2% total NGFB) and purified by cation-exchange chromatography and it yielded two bands on polyacrylamide-gel electrophoresis under nonreducing conditions, corresponding to the monomeric (14 kDa) and homodimeric (26.5 kDa) forms of the molecule. Both hNGFB forms were immunopositive on Western blots with rabbit anti-NGFB antibodies; however, following additional purification, only the species corresponding to the hNGFB homodimer was biologically active on cultured chicken dorsal root ganglion neurons. These results demonstrate the feasibility of synthesizing the biologically active form of hNGFB in E. coli.

Enhanced Secretion of Human Nerve Growth Factor from Saccharomyces cerevisiae using an Advanced δ–Integration System

We have designed an advanced delta-integration system (integration of genes into the delta-sequence of yeast retrotransposon Ty) and used it for secretion of human nerve growth factor (hNGF) from Saccharomyces cerevisiae. The expression and secretion of hNGF was directed by the PGK promoter and MF alpha 1 prepro-signal. Using two selectable markers (URA3 and leu2-d), haploid yeast strains were constructed with approximately 20 copies of a delta-integrated hNGF expression cassette on four chromosomes. The strain secreted hNGF at levels 3-4 fold higher than a 2 micron-based plasmid. Northern and Western analyses revealed that the oversecretion was caused by an increased amount of mRNA. We also detected an unusual processing of the MF alpha 1 prepro-hNGF fusion protein that required the pep4 mutation. Application of this system for industrial purposes is discussed.

Recombinant human beta-nerve growth factor (NGF): biological activity and properties in an enzyme immunoassay

Nerve growth factor (NGF) supports sympathetic and sensory neurons in the peripheral nervous system and also functions in the development and maintenance of cholinergic neurons in the basal forebrain. NGF distribution can be studied in the brain of the rat and mouse with the use of a sensitive two-site enzyme immunoassay (EIA) for mouse NGF. It would be of interest to measure the NGF protein also in the human brain, especially against the background that the cholinergic neurons are severely deteriorated in senile dementia of the Alzheimer type. The limited immunological cross-reactivity between NGFs from different species has previously hampered attempts to determine levels of the human NGF. We have now examined the biological activity and immunological properties of human recombinant NGF protein in medium conditioned by COS cells transfected with the human NGF gene. The human NGF behaved similar to mouse NGF in a sympathetic ganglion bioassay. The monoclonal antibody 27/21 to mouse NGF was shown to effectively block the activity of both the human recombinant NGF and mouse native NGF. A two-site EIA using monoclonal antibody 27/21 was optimized. Under the conditions used, the EIA detected the human recombinant NGF with the same sensitivity (1 pg/ml) as shown for the mouse NGF. It should now be possible to test this EIA also on homogenized tissue to examine human NGF in brain samples from Alzheimer patients and age-matched controls.

Human beta nerve growth factor obtained from a baculovirus expression system has potent in vitro and in vivo neurotrophic activity

A baculovirus expression vector, which contains the coding sequences for human prepro (beta) nerve growth factor under control of the viral polyhedrin promoter, was constructed. Upon infection of insect cells with the recombinant virus, mature human beta nerve growth factor (rhNGF) was released into the culture fluid. The mature rhNGF was biologically active since rat pheochromocytoma (PC12) and human neuroblastoma (SH-SY5Y) cells were induced to extend neurites upon treatment with this material. This activity was abolished by treating with antiserum prepared against mature mouse beta NGF (mNGF). When compared with mNGF, rhNGF more rapidly elicited the differentiation response in both PC12 and SH-SY5Y cells. In an in vivo assay of cholinergic cell survival, rhNGF was nearly as potent as mNGF in protecting cholinergic neurons from degeneration following a fimbria-fornix lesion. These results show that the baculovirus expression system provides quantities of biologically potent human beta NGF suitable for a comprehensive program of research to ascertain beta NGF's potential as a therapeutic agent for the treatment of Alzheimer's disease.

Production, purification and characterization of biologically active recombinant human nerve growth factor

The human NGF gene was isolated and inserted downstream from murine leukemia virus LTR in a plasmid having dihydrofolate reductase cDNA. The expression plasmid was introduced into CHO cells. Selection of the transformants for the resistance to methotrexate gave a CHO cell line which produced human NGF at a level of 4 mg/L in the culture medium. The recombinant human NGF was purified to near homogeneity from the culture supernatant. The NH2-terminal amino acid sequence, the COOH-terminal amino acid (Ala), and the amino acid composition of the human NGF were identical to those deduced from the nucleotide sequence of the human NGF gene. The recombinant human NGF was composed of 120 amino acid residues. Three disulfide linkages were determined to be Cys15-Cys80, Cys-58-Cys108, and Cys68-Cys110; the locations were identical to those in the mouse 2.5S NGF molecule. The specific biological activity of the recombinant human NGF was comparable with that of authentic mouse 2.5S NGF as determined by stimulation of neurite outgrowth from PC12 cells.

Integration of heterologous genes into the chromosome of Saccharomyces cerevisiae using a delta sequence of yeast retrotransposon Ty

Distribution of a delta (delta) sequence of the Ty element on a chromosome of the yeast Saccharomyces cerevisiae was analysed by pulsed-field gel electrophoresis. More than 100 copies of the delta sequence were nonrandomly distributed on the chromosome. Using the delta sequence as a recombination site, mouse alpha-amylase and human beta-endorphin genes were introduced into the chromosomal DNA. The integration occurred on a particular chromosome in each case and the copy number was estimated as three to five. It was also found that single- or multi-copy integration occurred at a single or multiple sites on the particular chromosome. The integrants secreted alpha-amylase and beta-endorphin by three-to fivefold compared with single-copy integrants. This type of integration was mitotically stable over a period of 50 generations under non-selective conditions.