The nature of the stimulatory role of the supernatant fraction on triglyceride synthesis by the alpha-Glycerophosphate pathway

Evidence is presented as to the nature and mechanism of the stimulatory effect of the supernatant fraction on the biosynthesis of triglycerides via the alpha-glycerophosphate pathway in the intestinal mucosa. When microsomes are employed as the enzyme source, the major lipid formed from either labeled palmitic acid orL: -alpha-glycerophosphate is phosphatidic acid and only a limited amount of triglyceride is synthesized. The addition of the supernatant fraction to microsomes results in a stimulation of triglyceride biosynthesis at the expense of phosphatidic acid. Employing the same microsomal fraction, the reaction sequence was followed step by step and the intermediates were isolated. The results suggest that the stimulatory role of the supernatant fraction can be attributed to the presence ofL: -alpha-phosphatidate phosphohydrolase (EC 3.1.3.4). The hydrolysis of the biosynthesized microsomal phosphatidic acid by the supernatant enzyme occurs at a faster rate than the hydrolysis of added phosphatidic acid prepared from egg lecithin. The initial acylation steps in the biosynthesis of triglycerides or phosphatidic acid via the glycerophosphate pathway occur only in the presence of fatty acid and the cofactors necessary for its activation. Under these conditions, fatty acyl-CoA will not substitute for the fatty acid activation system.

New approaches for the analysis of molecular recognition using the IAsys evanescent wave biosensor

Trends in the analysis of molecular recognition using the IAsys evanescent wave biosensor are outlined. Diversification of sensor surface chemistry, an open cuvette format and the advent of robotics controlled by intelligent software are widening the range and throughput of applications. Analyses of binding and dissociation are now carried out across a wide spectrum of biomolecules, including protein, nucleic acid, carbohydrate and lipid. Determinations are obtained from a range of experimental formats. These include qualitative 'yes/no' screening assays, through semi quantitative ranking of kinetic association, dissociation and equilibrium constants for a family of binding partners, to deriving constants comparable with those which would be obtained in free solution. A dependence of the initial rate of biomolecular association on concentration allows analyte concentration to be measured--an increasingly common application class. This is often employed in situations where a rapid determination is required The ability to recover bound analyte from the sensor surface in sufficient amounts for subsequent characterization is opening up new routes to the parallel analysis of structure and function.

Age, gender, and education may have little influence on error patterns in the assessment of set-shifting and rule induction among normal elderly

Error patterns have been found to be sensitive to cognitive status, but the relationship between aging and error patterns remains unclear, and may differ as a function of gender, education, and whether a task is verbal or nonverbal. The present study examined the error patterns of normal elderly individuals on a verbal measure of set-shifting and rule induction to determine whether demographic variables, that is, age, gender, and education, influenced test performance. The sample of 109 individuals, 38 males and 71 females, ranging in age from 54 to 89 years with 6 to 19 years of education, was assessed on the Classification subtest of the Test of Verbal Conceptualization and Fluency, a verbal measure of set-shifting and rule induction. Subjects' protocols were scored for perseverative, nonperseverative, and random errors, tabulated, and analyzed. Multivariate analysis of covariance with education as the covariate as well as other statistical tests revealed nonsignificant relationships between error scores and age, gender, and education. Years of education, however, showed a significant correlation with a reduction in random responses. Results are interpreted based on Horn's (1978) fluid-crystallized explanations of changes in intelligence with advancing age.

Bioprocess monitoring: an optical biosensor for rapid bioproduct analysis

The use of an optical biosensor for rapid bioproduct analysis is described. The biosensor, which is sensitive to changes in the concentration of bioproduct at its biologically active surface, has been shown to provide concentration data within 10 s of sample addition to the device. This has been achieved through the use of linear regression analysis to extract information from the early part of the biosensor interaction profiles. The system has been used to monitor both the production and purification of antibody fragments expressed during batch fermentation of recombinant Escherichia coli. Data obtained using the biosensor have been used to provide real-time profiles describing the location of antibody fragments during bioprocessing. Biosensor data have also been compared with those obtained from ELISA, the traditional method of retrospective analyses of samples collected during bioprocessing.

An optical biosensor for real-time chromatography monitoring: breakthrough determination

The use of an optical biosensor for immunorecognition of protein products during affinity chromatography is discussed to provide rapid data describing the loading and subsequent breakthrough, followed by elution and fraction collection. The optical biosensor works by following in real-time the interaction of soluble ligate with an appropriate ligand attached to the optically active surface. The initial rate of interaction between soluble ligate and immobilized ligand has been shown to correlate well with ligate concentration. This method of analysis has also been shown to agree well with ELISA, the traditionally employed technique for immunoassay of protein products lacking, for example, catalytic activity. Forward prediction, using models of the breakthrough fitted to the real-time data, has enabled the column saturation point to be determined before it has been reached, thus enabling appropriate action to ensure minimal loss of protein product while improving column utilization efficiency. The biosensor, operated within a flow injection analysis regime, has been demonstrated to provide concentration data within 10 s, with a total assay turnaround of 30 s.

Measurement of the kinetics of protein uptake by proximal tubular cells using an optical biosensor

BACKGROUND

The affinity and specificity of protein reabsorption by proximal tubular cells have been investigated using techniques for monitoring endocytosis, demonstrating a high capacity but low affinity process. It is not known whether uptake is through binding to a single binding site/receptor with differing affinities, or if there are several classes of binding sites receptors, each specific for differing proteins or groups, such as, high or low molecular weight proteins.

METHODS

We have developed a novel technique for analyzing the kinetics of protein binding to tubular cells using a optical biosensor system. We have studied the binding of cultured LLCPK cells to albumin and RBP immobilized onto the sensor. By adding increasing concentrations of competing proteins [varying in molecular weight from 66,000 to 11,800 D and pI from 4.6 to 9.2 as represented by albumin, alpha1-microglobulin (alpha1M), retinol binding protein (RBP), cystatin C and beta2-microglobulin (beta2m)], specific and inhibitable cell binding was demonstrated.

RESULTS

Equilibrium constants, KA, could be calculated from the reciprocal of the protein concentration causing 50% inhibition in binding rate. These were: albumin = 8.0 x 10(4) M(-1), alpha1M = 2.0 x 10(5) M(-1), RBP = 2.7 x 10(4) M(-1), cystatin C = 2.0 x 10(4) M(-1), beta2m = 4.2 x 10(3) M(-1). There were no significant differences between the measured KA's whether RBP or albumin were immobilized on the surface.

CONCLUSIONS

All the proteins gave similar shaped inhibition profiles, suggesting that there is one binding site/receptor for all proteins studied, regardless of molecular weight or charge, but there are differing affinities for each protein.

Ligand loading at the surface of an optical biosensor and its effect upon the kinetics of protein-protein interactions

Optical biosensors are finding increasing use in the determination of kinetic and equilibrium constants for a variety of biomolecular interactions. Usually these biosensors require one biomolecule, the ligand, to be covalently attached to a hydrogel matrix which itself is bonded to the sensing surface. The ligands partner, the ligate, then binds from solution resulting in a measurable change in response which the instrument records as a function of time. Although in many cases, optical biosensors are used in order to obtain parameters that relate to interactions in solution, it is becoming clear that measurements involving the interaction of ligate with immobilized ligands on surfaces require careful experimental design. Here we report on how the density of ligand loading within the hydogel matrix affects the measured interaction kinetics. It is found that crowding of ligand within this matrix results in a significant reduction in the measured association rate constant, with a corresponding effect in the calculated overall affinity. However, measurements at low ligand loadings show association rate constants that are comparable to those measured in solution. Clearly, where this comparison is required, it is important to perform measurements under such conditions.

An evaluation of practice leaflets provided by general dental practitioners working in multi-racial areas

AIM

The aim of this study was to assess the quality of information leaflets produced by NHS dental practices based in high density multi-racial areas within the city of Birmingham.

METHOD

All of the 41 general dental practices based in ten Birmingham electoral wards with high concentrations of ethnic minorities were approached for a copy of their practice leaflet. Each leaflet was assessed in terms of: 1. overall presentation, 2. general information, and 3. information specifically relevant to the ethnic minorities.

RESULTS

Seventy-eight per cent (32) of practices currently produce information leaflets. Compliance with specific NHS regulations ranged from 3% to 97%; 41% (13) of leaflets had one or more sections written in a minority language. Although ethnic minority languages were spoken by staff in three-quarters of the practices, less than one third specified this. Only one leaflet contained information on arrangements for non-English speaking patients.

CONCLUSION

Recommendations are made concerning the quality and content of practice leaflets for practices based in high density multi-racial areas.

Analysis of kinetic data of antibody-antigen interaction from an optical biosensor by exponential curve fitting

An optical biosensor system employing a resonant mirror (RM), with a stirred cuvette has been used to follow the interaction of a recombinant antibody fragment with its antigen, hen egg lysozyme. The data generated by the biosensor were analysed in order to determine the kinetic constants for the interaction using a linear transform (derivative analysis). For comparison the data were also analysed using an exponential curve fitting routine. It was demonstrated that the exponential curve fitting method produced results which were in agreement with the existing linear transform method. It was also shown that early fitting of the association phase response, using the exponential curve fitting routine between 0 and 70 s after sample addition, yielded sufficient information to provide a prediction of Kon. The potential use of the optical biosensor for the rapid monitoring of protein production and purification is discussed.

The secretion of active recombinant human gastric lipase by Saccharomyces cerevisiae

The expression of the complete human gastric lipase (HGL) gene in Saceharomyces cerevisiae grown in defined medium resulted in the secretion of active recombinant HGL (rec.HGL) to levels of up to approximately 11 mg/liter. Of the total measurable HGL activity, 90% was detected by assaying intact cells, suggesting that the majority of rec.HGL produced was secreted but stayed attached to the cell wall. The remaining 10% was present in the growth medium and from this source active rec.HGL was purified 300-fold by a combination of hydrophobic interaction and ion-exchange chromatography. Rec.HGL migrated on reduced SDS-PAGE as three bands with estimated molecular masses of 47,45, and 43 kDa. All three forms cross-reacted with an antibody raised to natural HGL and their treatment with Endo H showed them to be N-linked glycosylation variants of a single polypeptide. The 47-kDa species was isolated using lentil lectin Sepharose 4B and shown to possess a specific activity comparable to that of the natural enzyme. Rec.HGL had an acid pH activity optimum using either tributyrin or olive oil as substrate and did not lose activity if incubated in the presence of pepsin at pH 2.0. These results demonstrate that HGL secreted by Saccharomyces cerevisiae retained those properties of the natural enzyme required for its use in the treatment of pancreatic insufficiency.

Kinetics of protein-protein interactions at the surface of an optical biosensor

Methods based on the use of optical biosensors have recently become available to provide a convenient means of determining the rate and equilibrium constants for bimolecular interactions between immobilized ligands and soluble ligate molecules. However, the association data that these methods provide are not always accurately described by the expected pseudo-first-order reaction mechanism, particularly when the ligand is immobilized on a dextran matrix. We show that a better description of the association data, especially at higher ligate concentrations, is achieved with a double exponential function, indicating that at least two rate-limiting processes are involved. Various models are considered in order to explain these observations: the presence of two (or more) distinct populations of immobilized ligand; a change, possibly conformational, in the immobilized ligand before or after ligate binding; or the hindrance of ligate binding to immobilized ligand. We suggest that steric hindrance caused by ligate binding to the dextran-coated sensor surface seems the most likely explanation for the observed biphasic association kinetics and that the faster initial phase should be used in oder to determine association constants that can be compared to those in solution.

Development of T-cell leukaemia in an ataxia telangiectasia patient following clonal selection in t(X;14)-containing lymphocytes

Ataxia telangiectasia is a rare inherited and progressive neurological disorder in which patients show an unusual predisposition to T-cell leukaemia. We report here observations on a patient with a large cytogenetically abnormal clone showing a single t(X;14)(q28;q11) translocation which conferred a proliferative advantage on the cells. The further evolution of this clone to cytogenetically more complex clones of lymphocytes was seen in the patient. She subsequently developed a rapidly progressing T-cell leukaemia, with a CD4+CD8+ T-cell phenotype, about five years after the first appearance of additional chromosome translocations in the clone cells.

Denaturation studies on natural and recombinant bovine prochymosin (prorennin)

1. Prochymosin in solution in the presence of 8 M-urea is fully unfolded, as indicated by its fluorescence spectrum, fluorescence quenching behaviour and far-u.v.c.d. spectrum. 2. Equilibrium studies on the unfolding of prochymosin and pepsinogen by urea were carried out at pH 7.5 and pH 9.0. The results indicate that the stabilization energies of the two proteins are identical at pH 7.5, but that at pH 9.0 pepsinogen is significantly less stable than prochymosin. 3. Kinetic studies on the unfolding of prochymosin and pepsinogen indicate that the processes can be described by a single first-order rate constant, and that at any given value of denaturant concentration and pH the rate of unfolding of prochymosin is significantly greater than that of pepsinogen. 4. Unfolding of prochymosin by concentrated urea is not fully reversible, unlike that of pepsinogen. Kinetic analysis of the refolding of the proteins suggests the presence of a slow process following unfolding in urea; for pepsinogen this process leads to a slowly refolding form, whereas for prochymosin the slow process in urea leads to a form that cannot refold on dilution of the denaturant. 5. The results provide a rationale for an empirical process for recovery of recombinant prochymosin after solubilization of inclusion bodies in concentrated urea. 6. In all respects studied here, natural and recombinant bovine prochymosin were indistinguishable, indicating that the refolding protocol yields a recombinant product identical with natural prochymosin.

Correlation of gross and microscopic appearance of skin buttons in total artificial heart animals

Pneumatic artificial hearts are powered by compressed air that is delivered through percutaneous tubes. A stress relief device, termed a skin button, surrounds these tubes as they exit from the recipient's tissues. The skin button is designed to protect the tissues from damage and provide a secure material-tissue interface. Prevention of superficial and invasive infection is the primary goal of the skin button. Eight calves were studied prospectively to identify gross or microscopic infection with the skin button. All animals who survived more than sixty days (62-136) had both gross and microscopic evidence of infection. All animals surviving less than 60 days (13-43) had no gross evidence of infection but one had subcutaneous microscopic abscess formation. No animal died secondary to a skin button infection. Skin buttons cannot prevent infection but they can contain the pathologic process in the superficial tissues with no evidence of systemic effects.

Effect of a total artificial heart on adaptive hormonal responses in humans with end-stage heart failure

The J-7 total artificial heart (TAH) can restore normal vascular hemodynamics in humans treated for end-stage heart failure, but less is known regarding its effect on hormones elevated under these conditions. A 49-year-old man with NYHA Class IV end-stage heart failure received a J-7-70 TAH as a bridge to transplantation. Pre-TAH cardiac index was less than 2 L/min/m2 with end organ dysfunction, increased venous and pulmonary pressures, and a low arterial pressure. The TAH provided an immediate cardiac index greater than 3 L/min/m2 with normal hemodynamics and organ function. Pre-TAH renin, aldosterone, and atrial natriuretic factor (ANF) levels were markedly elevated: 147 ng/dl, 29.4 ng/dl, and 380 pg/ml, respectively. All values declined dramatically by the fifth postoperative day, with the aldosterone and ANF values returning to normal at 11.5 ng/dl and 37 pg/ml, respectively. Renin levels reached normal values by the fourth postoperative week. Once normal values were obtained, they remained in this range for the 57 days of TAH function. The TAH, used in end-stage heart failure, restores normal hemodynamics and compensatory hormonal levels. These hormones can be used as indicators of proper TAH function in such patients.

The role of beta receptors in the peripheral vasculature of calves with a total artificial heart

Drugs given to a total artificial heart (TAH) calf isolate their vascular effects independent of the myocardium. During experiments, the TAH maintains full ejection, constant heart rate, and percent systole, and uses no vacuum. Cardiac output (CO) varies solely and directly with preload. Six calves received an infusion of isoproterenol, a beta agonist, and three calves received propranolol, a beta antagonist. The isoproterenol was resumed after beta blockade. Isoproterenol alone caused a significant increase in CO, an effect that was attenuated but not eliminated with beta blockade. Both isoproterenol and propranolol decreased AoP, but only isoproterenol increased preload. Beta receptors play a significant role in decreasing venous capacitance with increased preload and CO, independent of the myocardium.

Molecular cloning of a human gastric lipase and expression of the enzyme in yeast

The molecular cloning of a cDNA coding for human gastric lipase and its expression in yeast is described. A lipase present in human gastric aspirates was purified and its N-terminal amino-acid sequence was determined. This was found to be homologous with the N-terminal sequence of rat lingual lipase. A cDNA library was constructed from mRNA isolated from human stomach tissue and probed with cloned rat lingual lipase DNA. One clone, pGL17, consisting of approximately 1450 base-pairs, contained the entire coding sequence for a human gastric lipase. The amino-acid sequence from the isolated protein and the DNA sequence obtained from the cloned gene indicated that human gastric lipase consists of a 379 amino acid polypeptide with an unglycosylated Mr of 43,162. Human gastric lipase and rat lingual lipase amino-acid sequences were closely homologous but were unrelated to porcine pancreatic lipase apart from a 6 amino-acid sequence around the essential Ser-152 of porcine pancreatic lipase. A yeast expression plasmid containing the phosphoglycerate kinase promoter and terminator sequences together with the human gastric lipase gene was constructed. Yeast transformed with this vector synthesised the lipolytically active enzyme.

Importance of human gastric lipase for intestinal lipolysis: an in vitro study

Using soybean triacylglycerols emulsified with egg lecithin we have studied, in vitro, the influence of substrate prehydrolysis by human gastric lipase upon subsequent degradation by the pancreatic lipase-co-lipase system. Fatty acids liberated by pure human gastric lipase or juice trigger immediate activity of human pancreatic lipase. Gastric lipolysis appears to be of prime importance for dietary lipid digestion in human.

Kinetic assay of human gastric lipase on short- and long-chain triacylglycerol emulsions

Under optimal conditions, assay for pure human gastric lipase was carried out with short- and long-chain triacylglycerol emulsions. Maximal specific activities of 1160 and 620 U/mg were obtained with tributyrin and soybean emulsion, respectively. We observed that with a tributyrin substrate, bovine serum albumin or bile salts must be added before the addition of the enzyme in order to prevent its irreversible interfacial denaturation. With long-chain triacylglycerols as substrate, a decrease with time in the rate of hydrolysis was associated with release of protonated long-chain fatty acids. The inhibitory effect of protonated fatty acids was also observed using tributyrin at pH 3.0. These observations support the conclusion that human gastric lipase shows no intrinsic specificity for short-chain triacylglycerols and that its apparent specificity is modulated by pH and presence of amphiphile in the incubation medium. Our conclusions support the view that, in the human, gastric lipolysis may play an important role in long-chain fat digestion.

Human gastric lipase. The effect of amphiphiles

Human gastric lipase (HGL) activity on tributyrin emulsion was detected only in the presence of amphiphiles such as bile salts, proteins (serum albumin, beta-lactoglobulin or ovalbumin) or phosphatidylcholine. These findings are contrary to the strong inhibitory effect of amphiphiles observed on pure pancreatic lipase. To reveal HGL activity, amphiphiles should be added prior to HGL. This may prevent irreversible interfacial denaturation. HGL activity was found to be restricted to a triacylglycerol/water surface tension ranging from 8 dyn/cm to 13 dyn/cm. All amphiphiles, which decrease the interfacial tension below 8 dyn/cm, act as irreversible inhibitors of HGL in the absence and in the presence of bile salts. Our results confirm that HGL is capable of hydrolysing triacylglycerol in the presence of the physiological concentration of bile salts prevailing in the upper small intestine and in the presence of alimentary proteins. These observations could explain the high dietary lipid absorption observed under pancreatic lipase deficiency.

Molecular cloning and nucleotide sequence of rat lingual lipase cDNA

Purified rat lingual lipase (EC3113), a glycoprotein of approximate molecular weight 52,000, was used to generate polyclonal antibodies which were able to recognise the denatured and deglycosylated enzyme. These immunoglobulins were used to screen a cDNA library prepared from mRNA isolated from the serous glands of rat tongue cloned in E. coli expression vectors. An almost full length cDNA clone was isolated and the nucleotide and predicted amino acid sequence obtained. Comparison with the N-terminal amino acid sequence of the purified enzyme confirmed the identity of the cDNA and indicated that there was a hydrophobic signal sequence of 18 residues. The amino acid sequence of mature rat lingual lipase consists of 377 residues and shares little homology with porcine pancreatic lipase apart from a short region containing a serine residue at an analogous position to the ser 152 of the porcine enzyme.

Efficient synthesis of enzymatically active calf chymosin in Saccharomyces cerevisiae

We have constructed a high-efficiency expression vector to direct the synthesis of heterologous polypeptides in yeast. The vector is termed a sandwich expression vector as the heterologous gene is inserted between the 5' and 3' control regions of the efficiently expressed yeast PGK gene. We have used this vector to direct the expression of three derivatives of the calf chymosin cDNA gene; preprochymosin, prochymosin and chymosin. Prochymosin is synthesised to at least 5% of total yeast-cell protein and furthermore, it can be readily activated to produce an enzyme which has milk-clotting activity.

Synthesis of calf prochymosin (prorennin) in Escherichia coli

A gene for calf prochymosin (prorennin) has been reconstructed from chemically synthesized oligodeoxyribonucleotides and cloned DNA copies of preprochymosin mRNA. This gene has been inserted into a bacterial expression plasmid containing the Escherichia coli tryptophan promoter and a bacterial ribosome binding site. Induction of transcription from the tryptophan promoter results in prochymosin synthesis at a level of up to 5% of total protein. The enzyme has been purified from bacteria by extraction with urea and chromatography on DEAE-cellulose and converted to enzymatically active chymosin by acidification and neutralization. Bacterially produced chymosin is as effective in clotting milk as the natural enzyme isolated from calf stomach.

Molecular cloning and nucleotide sequence of cDNA coding for calf preprochymosin

DNA complementary to calf stomach mRNA has been synthesised and inserted into the Pst1 site of pAT153 by G-C tailing. Clones containing sequences coding for prochymosin were recognised by colony hybridisation with cDNA extended from a chemically synthesised oligodeoxynucleotide primer, the sequence of which was predicted from the published amino acid sequence of calf prochymosin. Two clones were identified which together contained a complete copy of prochymosin mRNA. The nucleotide sequence is in substantial agreement with the reported amino acid sequence of prochymosin and shows that this protein has a mol.wt. of 40431 and chymosin a mol.wt. of 35612. The sequence also indicates that prochymosin is synthesised as a precursor molecule, preprochymosin, having a 16 amino acid hydrophobic leader sequence analogous to that reported for other secreted proteins.

The nucleotide sequence of cDNA coding for the structural proteins of foot-and-mouth disease virus

The complete nucleotide sequence of cDNA coding for the structural capsid polypeptides of foot-and-mouth disease virus (FMDV) (strain A(10)61) has been determined. Portions of the flanking sequence coding for the nonstructural proteins p20a and p52 are also provided. The three larger structural polypeptides VP1, VP2 and VP3 have unmodified Mrs of 23248, 24649 and 24213, respectively. The size of the smaller polypeptide, VP4, can only be estimated at 7360 because the 5'-limit of its coding region is not yet known with certainty. The sequence data for VP1 (the major immunising antigen) and the amino-terminal quarter of p52 are compared with the data of Kurz et al. (Nucl. Acids Res. 9 (1981) 1919-1931) for a different serotype (O1K). This shows that variation is much greater in the region coding for VP1 than in that coding for p52. This is reflected in the level of amino acid sequence variation predicted for the two proteins. Analysis of relative codon usage reveals a strong bias in favour of C and G over U and A in the third base position. The dinucleotide frequencies show a bias against A-U and U-A, and for A-C and C-A.

Temperature-sensitive RNA polymerase mutants of a picornavirus

Temperature-sensitive (ts) RNA polymerase mutants of a picornavirus are reported. Two foot-and-mouth disease virus (FMDV) mutants designated ts 22 and ts 115 have been characterized. As judged by isoelectric focusing, both have charge alterations in P56a, the FMDV RNA polymerase protein. Virus RNA synthesis in cells infected with the mutants is severely impaired at the nonpermissive temperature. RNA polymerase purified from baby hamster kidney cells infected with these mutants exhibits a marked ts transcribing activity in vitro. Spontaneous revertants of both mutants have P56a polypeptides that are indistinguishable from the parental proteins on the basis of charge. The revertants regain the ability to synthesize virus RNA in vivo at the nonpermissive temperature. RNA polymerase purified from the revertants remains transcriptionally active at the nonpermissive temperature.

Molecular cloning of foot and mouth disease virus genome and nucleotide sequences in the structural protein genes

Foot and mouth disease virus (FMDV), of the family Picornaviridae, consists of a single-stranded RNA (approximately 8,000 nucleotides), the translation of which is initiated on the 3' side of a 150-nucleotide poly(C) tract and yields a single polyprotein which is processed by host cell proteases into four primary products (Fig. 1). One or more virus-specified proteases further cleave these into the final products, the capsid proteins (VP1-4) being derived from the precursor p88 (for review see ref. 5). There are seven serotypes of the virus and as it has been shown that the immunizing activity of FMDV particles is associated primarily with VP1 (refs 6, 7), it seems likely that antigenic variation in FMDV is a result of changes in the structure of this protein. To further our understanding of this variation and as a first step in the possible development of FMDV vaccines from genetically manipulated microorganisms, we report here the construction and analysis of recombinant plasmids containing cDNA copies of the RNA. Comparison of the deduced amino acid sequence with the known polypeptide sequences shows that the NH2-termini of VP2 and VP3 are conserved between the A and O serotypes whereas that of VP1 (the immunizing antigen) varies by as much as 42% between serotypes.

In vitro thermal inactivation of a temperature-sensitive sigma subunit mutant (rpoD800) of Escherichia coli RNA polymerase proceeds by aggregation

A temperature-sensitive mutant sigma subunit (rpoD800) purified from Escherichia coli was inactivated in vitro by temperatures in excess of 37 degrees C whereas wild type sigma remained stable up to 49 degrees C. Both temperature-sensitive and wild type sigma formed multimeric aggregates upon thermal inactivation which were visualized by electron microscopy as polymeric chains. Conditions favoring sigma monomer (low sigma concentration and binding to core polymerase) protected temperature-sensitive sigma from heat inactivation. Full activity was recovered from inactivated temperature-sensitive sigma aggregates by incubation in a buffer containing 6 M guanidine HCl and subsequent removal of denaturant by dilution. Both wild type and temperature-sensitive sigma recovered full activity levels, retaining their characteristic thermal inactivation temperatures after denaturation in 6 M guanidine HCl and renaturation. Transcription of T4 DNA by RNA polymerase containing the rpoD800 mutant sigma subunit remained undiminished for 10 min after shift up to 46 degrees C but was almost completely inhibited within the following 10 to 15 min.

Isolation and characterization of transducing phage coding for sigma subunit of Escherichia coli RNA polymerase

A transducing phage has been isolated with codes for the sigma subunit of Escherichia coli RNA polymerase. Transducing phage were selected from E. coli shotgun collections of HindIII or Sac I fragments cloned into Charon 25, a new bacteriophage lambda vector that is capble of forming lyosogens at high temperature. Transduction of an E. coli strain carrying a temperature-sensitive mutation in the sigma gene was used for the selection. The positions of restriction sites for Sac I, HindIII, Xho I, Bgl II, and Kpn I in the cloned bacterial DNA segments were determined. Phage containing the HindIII fragment complement both primase (dnaG) and sigma (rpoD) whereas those containing the Sac I fragment complement only sigma. Results of analyses of the proteins made both in vivo after infection of UV-irradiated cells and in vitro in a coupled transcription/translation system suggest that a Sac I site separates the promoter for sigma from the sigma structural gene. The direction of transcription of sigma was determined to be clockwise with respect to the E. coli genetic map.

Altered chemical properties in three mutants of E. coli RNA polymerase sigma subunit

We have analyzed some chemical properties of the sigma subunit of RNA polymerase from the sigma mutants: rpoD1 (Gross et al., 1978), rpoD2 (formerly known as alt-1) (Silverstone et al., 1972; Travers et al., 1978), and rpoD800 (Gross et al., 1979). Each of the three mutants is located at about 66 min on the E. coli genetic map and exhibits an alteration in the enzymatic properties of its sigma subunit. The tryptic peptides and isoelectric focusing behavior were analyzed for mutant and wild type sigma. A single, but different altered lysine tryptic peptide was observed for each mutant. No altered arginine tryptic peptides were observed. The rpoD800 mutant sigma showed an altered isoelectric point. These studies provide chemical evidence that the sigma polypeptide in all three mutants is altered and strongly support the conclusion that the mutations are in the structural gene for sigma.

Purification and properties of the sigma subunit of Escherichia coli DNA-dependent RNA polymerase

An improved purification procedure is described for the sigma subunit of escherichia coli DNA-dependent RNA polymerase [ribonucleoside triphosphate:RNA nucleotidyl-transferase, EC 2.7.7.6]. The method involves chromatography of purified RNA polymerase on single-stranded DNA-agarose, Bio-Rex 70, and finally Ultragel AcA44. The sigma factor obtained is electrophoretically pure with a yield of about 40%. A number of the chemical--physical properties of sigma are presented. A molecular weight of 82,000 was determined by phosphate buffered sodium dodecyl sulfate--polyacrylamide gel electrophoresis. Ultraviolet absorption spectra were used to determine an E280nm 1% of 8.4. The amino acid composition and 12-residue N-terminal sequence (Met-Glx-Glx-Asx-Pro-Glx-(Ser or Cys)-Glx-Leu-Lys-Leu-Leu) of sigma have been determined. The isoelectric focusing properties of sigma are presented. Denaturation--renaturation studies indicate that sigma is capable of an unusually rapid and complete recovery of activity after being subjected to denaturing conditions. A stable, 40,000-dalton fragment is generated from sigma by mild trypsin treatment.

The dissociation of sigma-factor from ribonucleic acid polymerase

The sigma-factor of Escherichia coli RNA polymerase was shown to dissociate from the core enzyme as a function of absolute concentration. The association constant is in the range 10(6)-10(8) litre/mol. This implies that the amount of holoenzyme, core enzyme and sigma-factor in RNA polymerase assays may vary according to the absolute concentration of the enzyme.

Rifampicin binding as a probe for subunit interactions in Escherchia coli RNA polymerase

The binding of the inhibitor rifampicin to RNA polymerase (alpha2betabeta') and its deficient subunit mixtures was investigated. The ability of beta to bind stoichiometric amounts of rifampicin was restored by formation of the alpha2beta subassembly. beta,beta' alpha, betabeta' and alpha2beta' were unable to bind rifampicin. RNA polymerase denatured with 6 M guanidine hydrochloride and dialysed against a renaturing buffer at 0degrees C ("renatured inactive enzyme") bound stoichiometric amounts of rifampicin but had lost the ability of bind dna. compared with native RNA polymerase "renatured inactive" enzyme possessed a markedly different tertiary structure as judged by limited proteolysis.