Pregnenolone metabolized to 17alpha-hydroxyprogesterone in yeast: biochemical analysis of a metabolic pathway

The cDNA coding for the human 3beta-hydroxy-5-ene steroid dehydrogenase/5-ene-4-ene steroid isomerase (3beta-HSD) has been expressed in yeast. When expressed from identical vectors except for the coding sequence, the specific activity of the type I is lower than that of the type II enzyme. A mutant of the human 3beta-HSD type II lacking the putative membrane spanning domain 1 was generated by site directed mutagenesis: its apparent K(m) for pregnenolone (PREG) is significantly increased and its V reduced to the level of the type I enzyme. The influence of the kinetic properties of 3beta-HSD in the accumulation of 17alpha-hydroxyprogesterone was probed by co-expression of the bovine 17alpha-hydroxylase cytochrome P450 (P45017alpha) cDNA. The metabolism of PREG was followed with time using the membrane fraction. Kinetic properties of the 3beta-HSD were modulated such that its activity was in excess, limiting or balanced with respect to the activity of the P45017alpha and the accumulation of intermediates and products recorded. Conditions for the generation of the by-products resulting from the 17,20-Lyase activity of the P45017alpha were found. The potential applications of the system are discussed.

Pregnenolone esterification in Saccharomyces cerevisiae. A potential detoxification mechanism

While studying the effect of steroids on the growth of the yeast Saccharomyces cerevisiae, we found that pregnenolone was converted into the acetate ester. This reaction was identified as a transfer of the acetyl group from acetyl-CoA to the 3beta-hydroxyl group of pregnenolone. The corresponding enzyme, acetyl-CoA:pregnenolone acetyltransferase (APAT) is specific for Delta5- or Delta4-3beta-hydroxysteroids and short-chain acyl-CoAs. The apparent Km for pregnenolone is approximately 0.5 microm. The protein associated with APAT activity was partially purified and finally isolated from an SDS/polyacrylamide gel. Tryptic peptides were generated and N-terminally sequenced. Two peptide sequences allowed the identification of an open reading frame (YGR177c, in the S. cerevisiae genome database) translating into a 62-kDa protein of hitherto unknown function. This protein encoded by a gene known as ATF2 displays 37% identity with an alcohol acetyltransferase encoded by the yeast gene ATF1. Disruption of ATF2 led to the complete elimination of APAT activity and consequently abolished the esterification of pregnenolone. In addition, a toxic effect of pregnenolone linked to the disruption of ATF2 was observed. Pregnenolone toxicity is more pronounced when the atf2-Delta mutation is introduced in a yeast strain devoid of the ATP-binding cassette transporters, PDR5 and SNQ2. Our results suggest that Atf2p (APAT) plays an active role in the detoxification of 3beta-hydroxysteroids in association with the efflux pumps Pdr5p and Snq2p.

Sterol uptake in Saccharomyces cerevisiae heme auxotrophic mutants is affected by ergosterol and oleate but not by palmitoleate or by sterol esterification

The relationship between sterol uptake and heme competence in two yeast strains impaired in heme synthesis, namely, G204 and H12-6A, was analyzed. To evaluate heme availability, a heterologous 17alpha-hydroxylase cytochrome P-450 cDNA (P-450c17) was expressed in these strains, and its activity was measured in vivo. Heme deficiency in G204 led to accumulation of squalene and lethality. The heterologous cytochrome P-450 was inactive in this strain. The leaky H12-6A strain presented a slightly modified sterol content compared to that for the wild type, and the P-450c17 recovered partial activity. By analyzing sterol transfer on nongrowing cells, it was shown that the cells were permeable toward exogenous cholesterol when they were depleted of endogenous sterols, which was the case for G204 but not for H12-6A. It was concluded that the fully blocked heme mutant (G204) replenishes its diminishing endogenous sterol levels during growth by replacement with sterol from the outside medium. Endogenous sterol biosynthesis appears to be the primary factor capable of excluding exogenous sterol. Oleate but not palmitoleate was identified as a component that reduced but did not prevent sterol transfer. Sterol transfer was only slightly affected by a lack of esterification. It is described herein how avoidance of the potential cytotoxicity of the early intermediates of the mevalonate pathway could be achieved by a secondary heme mutation in erg auxotrophs.

Self-sufficient biosynthesis of pregnenolone and progesterone in engineered yeast

The first two steps of the steroidogenic pathway were reproduced in Saccharomyces cerevisiae. Engineering of sterol biosynthesis by disruption of the delta 22-desaturase gene and introduction of the Arabidopsis thaliana delta 7-reductase activity and coexpression of bovine side chain cleavage cytochrome P450, adrenodoxin, and adrenodoxin reductase, lead to pregnenolone biosynthesis from a simple carbon source. Following additional coexpression of human 3 beta-hydroxysteroid dehydrogenase/isomerase, pregnenolone is further metabolized to progesterone. Steroid formation appears to be coupled to yeast sterol biosynthesis.

Probing the limits of expression levels by varying promoter strength and plasmid copy number in Saccharomyces cerevisiae

Heterologous gene expression levels were measured in yeast using the Escherichia coli gusA gene (encoding beta-D-glucuronidase) as a reporter. The influence of two major parameters, promoter activity and plasmid copy number, was studied. (1) Promoters used in this study ranged from the very weak constitutive KEX2, the regulated CYC1 and PGK and the mating type-specific MF alpha 1 to the strong constitutive TEF1 and TDH promoters. Using centromeric vectors, gusA expression levels varied within three orders of magnitude. (2) Plasmid copy number was changed by shifting from a monocopy (centromeric plasmid) over a moderate copy number (2 mu-based plasmid) to a high copy number (2 mu associated with the URA3-d selection marker). gusA expression levels increased relatively with plasmid copy number in all cases studied, but did not exceed the equivalent of 2% of total soluble yeast proteins. Coupling these variables, a 5-log range in gene expression levels was covered. Taken together, these results provide a framework which allows a comparison of existing and new promoters. This framework will be useful for expressing genes to required levels.

Efficient generation of recombinant adenovirus vectors by homologous recombination in Escherichia coli

Despite recent technical improvements, the construction of recombinant adenovirus vectors remains a time-consuming procedure which requires extensive manipulations of the viral genome in both Escherichia coli and eukaryotic cells. This report describes a novel system based on the cloning and manipulation of the full-length adenovirus genome as a stable plasmid in E. coli, by using the bacterial homologous recombination machinery. The efficiency and flexibility of the method are illustrated by the cloning of the wild-type adenovirus type 5 genome, the insertion of a constitutive promoter upstream from the E3 region, the replacement of the E1 region by an exogenous expression cassette, and the deletion of the E1 region. All recombinant viral DNAS were shown to be fully infectious in permissive cells, and the modified E3 region or the inserted foreign gene was correctly expressed in the infected cells.

11 beta-hydroxylase activity in recombinant yeast mitochondria. In vivo conversion of 11-deoxycortisol to hydrocortisone

In mammals, the final 11 beta-hydroxylation step of the hydrocortisone biosynthesis pathway is performed by a mitochondrial enzyme, namely cytochrome P-450(11 beta), together with the electron carriers adrenodoxin and NADPH adrenodoxin oxidoreductase. Successful production of a functional steroid 11 beta-hydroxylase activity was obtained in recombinant yeast in vivo. This conversion was achieved by coexpression of a mitochondrially targeted adrenodoxin and a modified bovine P-450(11 beta) whose natural presequence was replaced by a yeast presequence, together with an unexpected yeast endogenous NADPH-adrenodoxin-reductase-like activity. Adrenodoxin and P-450(11 beta) behave as a mitochondrial matrix and membrane protein, respectively. Saccharomyces cerevisiae apparently produces a mitochondrial protein which is capable of transferring electrons to bovine adrenodoxin, which in turn transfers the electrons to P-450(11 beta). The endogenous adrenodoxin oxidoreductase gains electrons specifically from NADPH. The notion that a yeast microsomal NADPH P-450 oxidoreductase can transfer electrons to mammalian microsomal P-450s can be extended to mitochondria, where an NADPH adrenodoxin oxidoreductase protein transfers electrons to adrenodoxin and renders a mitochondrial mammalian P-450 functional in vivo. The physiological function of this yeast NADPH adrenodoxin oxidoreductase activity is not known.

In vivo intermolecular recombination in Escherichia coli: application to plasmid constructions

Repair of a double-strand break (DSB) was investigated by intermolecular recombination in Escherichia coli (Ec) recBC sbcBC cells with restriction enzyme-cleaved model plasmids. Circular plasmids were generated when a linearized plasmid (vector) containing an origin of replication was co-transformed with a DNA fragment (template) containing a homologous sequence. The influence of the position of the DSB in the vector was analyzed using templates which contain various genetic markers, non-homologous sequences and/or deletions relative to the vector. In all cases, when a DSB occurs within a marker, this marker is lost in the resulting plasmid, whereas markers flanked by homologous regions located in the vicinity of a DSB are transmitted. Insertions (deletions), substitutions and shuffling of genetic markers are possible by in vivo recombination using Ec and can be applied to plasmid constructions. It is shown that recombination can occur from both template ends or from one vector and one template end. A D-loop nuclease is suggested to participate in the resolution of the recombination intermediates.

A human SP-C promoter fragment targets alpha 1-proteinase inhibitor gene expression to lung alveolar type II cells in transgenic mice

A 1.277 kb promoter fragment of the gene encoding one of the lung surfactant proteins, SP-C, was cloned from a human genomic library and characterized using the human alpha 1-proteinase inhibitor (alpha 1PI) gene as reporter. Messenger RNA for human alpha 1PI isolated from a single transgenic mouse line was detected solely in lung tissue. Using immunogold electron microscopy, accumulation of human alpha 1PI was shown unambiguously to occur only in type II pulmonary cells and, in discrete amounts, in the alveolar lining fluid. The protein was secreted and glycosylated showing a molecular weight close to that of plasma-derived human alpha 1PI.

In vivo cloning by homologous recombination in yeast using a two-plasmid-based system

In order to reduce the number of classical DNA manipulation and ligation steps in the generation of yeast expression plasmids, a series of vectors is described which facilitate the assembly of such plasmids by the more efficient 'recombination in vivo' technique. Two sets of vectors were developed. The first set, called 'expression vectors', contains an expression cassette with a yeast promoter and the PGK terminator separated by a polylinker, and an Escherichia coli replicon. Subcloning in these vectors of a DNA fragment generates a 'transfer vector' which is compatible with the second set of E. coli-yeast shuttle vectors. This set of 'recombination vectors' contains a cassette for a functional copy of a gene complementing a host strain auxotrophy or a bacterial gene conferring an antibiotic resistance to the plasmid-bearing host. Plasmid copy numbers can be modulated through the use of URA3 or URA3-d as the selective marker together with an ARS/CEN and the 2 microns replicon. Integration of the cloned DNAs into the yeast linearized replicative vectors occurs by recombination between homologous flanking sequences during transformation in yeast or E. coli. All the vectors contain the origin of replication of phage f1 and allow the generation of single-stranded DNA in E. coli for sequencing or site-directed mutagenesis.

Evaluation of Escherichia coli recBC sbcBC mutants for cloning by recombination in vivo

In vivo recombination as a tool for plasmid construction was analyzed using a model system based on the properties of the RecF pathway in Escherichia coli. This pathway was used after a double strand break (DSB) effected by restriction enzyme cleavage of the plasmids of interest. DSB repair was shown to be independent of the methylation state of the vector or insert DNA, of the type of restriction enzyme used (5' or 3' overhanging or blunt ends) and of dephosphorylation of the vector and/or template. Since the E. coli repair system does not recognize insertions, this recombination mechanism can be used to exchange cDNAs between different vectors. Some implications of the results on the mechanism of recombination are discussed.

Expression of alpha 1-proteinase inhibitor in Escherichia coli: effects of single amino acid substitutions in the active site loop on aggregate formation

Overproduction of eukaryotic proteins in microorganisms often leads to the formation of insoluble protein aggregates which accumulate as intracellular inclusion bodies. alpha 1-Proteinase inhibitor (alpha 1-PI) when produced as a cytoplasmic protein in Escherichia coli (E. coli) forms inclusion bodies containing the majority of the inhibitor in an inactive form. Several variants of alpha 1-PI with single amino acid substitutions within their active site loop (amino acids 345-358) were produced in a bioreactor showing that substitution of Met351 with Glu resulted in significantly reduced aggregate formation compared to the other variants and to wild-type protein. In addition, this variant proved to be fully functional as a proteinase inhibitor. Based on these findings and on results of previous structural studies a mechanism for aggregate formation during expression of alpha 1-PI is suggested.

Addition of a dipeptide spacer significantly improves secretion of ovine trophoblast interferon in yeast

Yeast has been analysed for its potential to secrete an ovine member of the type-I interferon (IFN) family, trophoblastin (oTP-1). The processing potential of the yeast KEX2 gene product (KEX2p) was evaluated using gene oTP-1 fused to the pre-pro sequence encoding the pre-pro peptide of the yeast alpha-factor precursor. High-level accumulation of nonprocessed (unmatured) recombinant oTP-1 (re-oTP-1) was observed in the medium. In order to short-circuit the limiting activity of KEX2p and to obtain a fully matured re-oTP-1, secretion was directed using a pre::oTP-1 fusion, relying only on signal peptidase-dependent processing. However, secretion of oTP-1 was impaired. High-level secretion was restored when the gene product contained a peptide spacer between oTP-1 and the signal peptidase cleavage site. The oTP-1 variant was shown to have an extended N terminus. An N-extended form was examined further and shown to have the correct size. Surprisingly, the variant retained its in vitro and in vivo biological activities. This system is likely to represent a general method for high-level secretion of type-I IFNs.

A 17.6 kbp region located upstream of the rabbit WAP gene directs high level expression of a functional human protein variant in transgenic mouse milk

We have investigated whether DNA regions present in the rabbit whey acidic protein (WAP) promoter/5' flanking sequence could potentially confer, in vivo, high level expression of reporter genes. Transgenic mice were generated expressing a variant of human alpha 1-antitrypsin, which has inhibitory activity against plasma kallikrein under the control of a 17.6 kbp DNA fragment located upstream of the rabbit WAP gene. Up to 10 mg/ml of active and correctly processed recombinant protein were detected in mouse milk, thus suggesting that the far upstream DNA sequences from the rabbit WAP gene might be useful for engineering efficient protein production in the mammary glands of transgenic animals.

Inhibitory activity and conformational transition of alpha 1-proteinase inhibitor variants

Several variants of alpha 1-proteinase inhibitor (alpha 1-PI) were investigated by spectroscopic methods and characterized according to their inhibitory activity. Replacement of Thr345 (P14) with Arg in alpha 1-PI containing an Arg residue in position 358 (yielding [Thr345----Arg, Met358----Arg]alpha 1-PI) results in complete loss of its inhibitory activity against human alpha-thrombin; whereas an exchange of residue Met351 (P8) by Glu [( Met351----Glu, Met358----Arg]alpha 1-PI) does not alter activity. [Thr345----Arg, Met358----Arg]alpha 1-PI is rapidly cleaved by thrombin, while [Met358----Arg]alpha 1-PI and [Met351----Glu, Met358----Arg]alpha 1-PI form stable proteinase-inhibitor complexes. The stability of [Thr345----Arg, Met358----Arg]alpha 1-PI against guanidinium chloride denaturation is significantly enhanced compared to wild-type alpha 1-PI, and does not change after cleavage, resembling ovalbumin, a serpin with no inhibitory activity, from which the Thr345----Arg amino acid exchange had been derived. [Met351----Glu, Met358----Arg]alpha 1-PI and [Met358----Arg]alpha 1-PI resemble the wild-type protein in this respect. The CD spectra of intact and cleaved alpha 1-PI variants do not compare well with the wild-type protein, probably reflecting local structural differences. Insertion of a synthetic peptide, which corresponds to residues Thr345----Met358 of human alpha 1-PI, leads to the formation of binary complexes with all variants having the characteristic features of the binary complex between peptide and wild-type protein.

Polymorphism in the dgt-dapD-tsf region of Escherichia coli K-12 strains

Restriction analysis of the dapD region cloned from several strains of Escherichia coli, revealed a restriction-fragment length polymorphism (RFLP). This RFLP, which includes the BamHI, EcoRI and SalI sites, may be useful in classification of various E. coli strains.

Development of stable, genetically well-defined conditionally viable Escherichia coli strains

The diaminopimelate (DAP) pathway provides the cell with lysine and with DAP, a vital cell wall constituent. Mutations in the DAP pathway of lysine biosynthesis are lethal for cells exposed to lysine in the absence of DAP. In this paper, the substitution of the dapD gene of Escherichia coli with the kanamycin resistance gene from Tn903 is described and its possible uses are discussed.

Stability of a host-vector system based on complementation of an essential gene in Escherichia coli

Antibiotic selection is the most common selection system for plasmid-containing bacteria. This technique, nevertheless, can be a source of problems during the expression of heterologous genes in Escherichia coli. We have developed an alternative selection system based on the complementation of a chromosomal auxotrophic (dapD2) mutation by the corresponding wild type gene carried on a plasmid. We show that the system effectively selects for the presence of plasmid on solid and liquid medium. In addition, we have observed a loss of viability associated with high levels of gene expression and accumulation of a heterologous protein, but the selective power and improved intrinsic stability of the dap+ plasmid, compared to a beta-lactamase (bla) based vector, excludes overgrowth of the culture by plasmidless cells.

Evidence for extended maintenance of the corpus luteum by uterine infusion of a recombinant trophoblast alpha-interferon (trophoblastin) in sheep

Ovine trophoblastin (oTP) is a natural interferon of the class-II interferon-alpha subfamily. Recombinant ovine trophoblastin (r.oTP), produced by genetic engineering, was purified by anion-exchange HPLC. The product exhibited a high degree of homogeneity (greater than 98%), and similar immunological cross reaction and antiviral activity to natural oTP. Antiluteolytic activity of r.oTP was established by intrauterine injection in two groups of cyclic recipient ewes. Control group A included 10 ewes which received sterile BSA in saline twice daily for 8 days (from day 10-12 of oestrous cycle). Experimental group B included 17 ewes which received 80 micrograms (4 ewes), 170 micrograms (8 ewes) or 340 micrograms (5 ewes) r.oTP daily for 8 days. Maintenance of functional corpora lutea for 1 month or more was observed in 4 out of 5 ewes which received high doses of r.oTP. These results indicate that oTP alone extends luteal secretory activity.

Influence of the second and third codon on the expression of recombinant hirudin in E. coli

The effect of all possible codons corresponding to the second and third amino acid (isoleucine and threonine) on the expression level of hirudin in E. coli has been analysed. These levels could not be correlated with changes in primary and secondary mRNA structure. A decrease in the rate of synthesis and of product accumulation follows the introduction for ile of the ATA codon which is of very low usage, and for thr of the ACC codon, which results in homology of the mRNA with the 3'-end of 16S rRNA. The results are discussed according to current concepts of protein expression in E. coli.

Conversion of recombinant hirudin to the natural form by in vitro tyrosine sulfation. Differential substrate specificities of leech and bovine tyrosylprotein sulfotransferases

Hirudin, a tyrosine-sulfated protein secreted by the leech Hirudo medicinalis, is one of the most potent anticoagulants known. The hirudin cDNA has previously been cloned and has been expressed in yeast, but the resulting recombinant protein was found to be produced in the unsulfated form, which is known to have an at least 10 times lower affinity for thrombin than the naturally occurring tyrosine-sulfated hirudin. Here we describe the in vitro tyrosine sulfation of recombinant hirudin by leech and bovine tyrosylprotein sulfotransferase (TPST). With both enzymes, in vitro sulfation of recombinant hirudin occurred at the physiological site (Tyr-63) and rendered the protein biochemically and biologically indistinguishable from natural hirudin. However, leech TPST had an over 20-fold lower apparent Km value for recombinant hirudin than bovine TPST. Further differences in the catalytic properties of leech and bovine TPSTs were observed when synthetic peptides were tested as substrates. Moreover, a synthetic peptide corresponding to the 9 carboxyl-terminal residues of hirudin (which include Tyr-63) was sulfated by leech TPST with a similar apparent Km value as full length hirudin, indicating that structural determinants residing in the immediate vicinity of Tyr-63 are sufficient for sulfation to occur.

Inhibition by recombinant hirudins of experimental venous thrombosis and disseminated intravascular coagulation induced by tissue factor in rats

Antithrombotic potency of recombinant hirudins rHV2, rHV2-Lys47 and rHV2-Arg47 was studied in a model of experimental thrombosis induced by tissue factor in the rat. Venous thrombosis was induced by i.v. injection of 25 mg/kg tissue factor followed by stasis of the inferior vena cava. In this model natural recombinant hirudins, rHV2 and rHV2-Lys47 injected 5 min before thrombo-plastin totally inhibited thrombosis in the same micrograms range as heparin or natural hirudin extracted from leeches. However, the mutant variant rHV2-Arg47 gave a maximal 60% inhibition of thrombosis. Variants rHV2-Lys47 (30 micrograms/kg) and rHV2-Arg47 (157 micrograms/kg) injected 5 min before thromboplastin prevented by 90 to 100% the drop in platelet count observed during the disseminated intravascular coagulation induced by thromboplastin injection. Recombinant hirudins were less anticoagulant than heparin as measured by an APTT on rat plasma. After rat tail transection, rHV2-Lys47 caused a 2-fold smaller prolongation of the bleeding time than an equivalent antithrombotic dose of heparin. Plasmatic elimination of rHV2-Lys47 from rat plasma after i.v. injection had a fast distribution phase with a half-life of 3 min during which 90% of injected rHV2-Lys47 was lost and was followed by a slower elimination phase. Thus recombinant hirudin rHV2-Lys47 appears as a promising potent antithrombotic agent for the prevention of thrombin-dependent venous thrombosis and disseminated intravascular coagulation.

Production and evaluation of recombinant hirudin

Hirudin, a 65 amino acid polypeptide form the medicinal leech, is an extremely efficient and specific thrombin inhibitor whose therapeutic potential has been demonstrated in a number of animal models. We have developed protocols for the production of recombinant hirudin by secretion from S. cerevisiae and carried out a full biologic evaluation of the purified product. These studies showed that natural and recombinant hirudin was similar in structure and in biologic function in vitro. Moreover, the recombinant protein displayed strong antithrombotic activity in several experimental thrombosis models in vivo, confirming the molecule's promise in the therapy of thrombotic disorders.

Point mutations modifying the thrombin inhibition kinetics and antithrombotic activity in vivo of recombinant hirudin

The hirudin variant HV2 was modified by in vitro site-specific mutagenesis of HV2 cDNA to generate HV2(Asn-47----Lys), HV2(Asn-47----Arg) and HV2(Lys-35----Thr, Asn-47----Lys). Residues 35 and 47 are positioned respectively within the finger and prothrombin-like domains of hirudin, both of which have been suggested as thrombin binding sites. The modified polypeptides were synthesized in Saccharomyces cerevisiae using a secretion vector and purified from culture supernatants. By analysis of the human alpha-thrombin:hirudin inhibition reaction in steady-state conditions it was shown that the dissociation constants for HV2(Lys-47) and HV2(Arg-47) were 5- to 14-fold lower than for unmodified HV2, whereas mutation of Lys-35 did not significantly alter the inhibition kinetics. Furthermore, HV2(Lys-47), whose sequence is identical to a natural hirudin variant, displayed enhanced anti-thrombotic activity in vivo, having a 100-fold lower ED50 compared to HV2 in the rabbit Wessler venous thrombosis model. These results support a role for the prothrombin-like domain in thrombin binding and, moreover, demonstrate that in vivo antithrombotic efficiency correlates with the dissociation constant of the inhibition reaction.

Use of human surfactant low molecular weight apoproteins in the reconstitution of surfactant biologic activity

Two low molecular weight (LMW) apoproteins were isolated from human pulmonary surfactant. SDS polyacrylamide gel analysis showed one protein (SP 18) to have an apparent molecular weight of 18,000 when unreduced and 9,000 D after reduction. The second protein (SP 9) migrated at approximately 9,000 D in the presence or absence of reducing agents. Both proteins contain a high number of hydrophobic amino acids. The NH2-terminal sequence of SP 18 was determined to be: NH2-phe-pro-ile-pro-leu-pro-tyr-. A cDNA clone isolated from a human adult lung cDNA library contained a long open reading frame encoding at an internal position the human SP 18 amino-terminal sequence. Mixtures of phospholipids (PL) and SP 9 and SP 18 were assessed for their capacity to reduce surface tensions on a pulsating bubble surfactometer. The addition of 1% apoprotein resulted in a reduction of surface tension after 15 s from 42.9 dyn/cm for PL alone to 16.7 and 6.3 dyn/cm for preparations containing SP 9 and SP 18, respectively. In vivo assessment of reconstituted surfactant activity was performed in fetal rabbits. Reconstituted surfactant consisting of PL + 0.5% SP 18 instilled intratracheally at delivery resulted in a marked increase in lung compliance, while the incorporation of 0.5% SP 9 yielded a moderate increase. These data show the ability to produce biologically active surfactant by the addition of isolated LMW apoproteins to defined PL.

Cloning and expression of a cDNA coding for the anticoagulant hirudin from the bloodsucking leech, Hirudo medicinalis

Cloned cDNAs have been isolated that encode a variant of hirudin, a potent thrombin inhibitor that is secreted by the salivary glands of the medicinal leech, Hirudo medicinalis. This variant probably corresponds to a form that has been purified from leech heads but differs in amino acid sequence from the hirudin purified from whole leeches. There are at least three hirudin transcripts detectable in leech RNAs that are different in size, site of synthesis, inducibility by starvation, and relationship to hirudin activity. The new hirudin variant predicted by the cDNA and the heterodisperse transcription products suggest a hirudin protein family. The hirudin cDNA was expressed in Escherichia coli under the control of the bacteriophage lambda PL promoter. The recombinant product is biologically active, inhibiting the cleavage by thrombin of fibrinogen and a synthetic tripeptide substrate.

Use of synthetic oligonucleotides in gene isolation and manipulation

Great progress has occurred in the techniques of synthesis of DNA molecules of defined sequences in terms of speed, length of the obtained oligonucleotides, and automation of the processes. Corresponding progress also occurred in the ways of using synthetic DNA in molecular biology and recombinant DNA research. Screening of cloned DNA sequence banks with long, unique oligonucleotides, provided a new approach to isolate the genes for proteins which are present in very small quantity. This technique can present considerable advantages over the more classical use of mixtures of oligonucleotides, in reducing the number of potentially positive clones on a primary screen, and enabling cloning with a minimum of amino acid sequence data. Synthetic oligonucleotides also provide the basis of a set of techniques for site-directed mutagenesis of DNA sequences. This allows the possibility of engineering the structure of particular proteins, and the properties of new variants can be tested by expressing the protein in a heterologous host. An example of this approach is the production of variants of human alpha 1-antitrypsin. A variant where valine replaces the methionine at the active site is equally active as an antielastase, but no longer susceptible to oxidative inactivation. A second variant, where arginine replaces the methionine, now functions as an antithrombin, but no longer inhibits elastase. Total gene synthesis is now feasible for larger and larger genes, and some of the recent strategies of whole gene synthesis are presented.

A comparative analysis of extreme thermophilic bacteria belonging to the genus Thermus

Several extreme thermophilic Gram negative bacteria found in a thermally polluted river in Belgium have been compared with Thermus strains isolated from widely distant geographical areas. This analysis has become possible after the design of a new culture medium (162). All strains examined (including the isolate successively denominated Flavobacterium thermophilum and Thermus thermophilus) were found to be morphologically identical with strain YT-1 of Thermus aquaticus. The cells are immotile, rod-like, strictly aerobic, catalase and oxidase positive. They produce amylase, hydrolyze gelatin and are confirmed to be highly sensitive towards penicillin. The nutritional pattern of all strains has been analysed extensively, by testing a broad spectrum of possible substrates. The strains display a uniform response to the microbiological tests applied and most probably belong to the same species: Thermus aquaticus.