[A voltage-clamp study on voltage-gated calcium channels translated in Xenopus oocytes by rat brain mRNA]

Voltage-gated calcium channels, expressed in Xenopus oocytes after injection of rat brain mRNA, were studied by using voltage-clamp technique. The properties of the calcium channels were characterized by barium current (IBa) passed through the channels. All oocytes used in this study were taken from five identified donors. Endogenous voltage--activated barium current measured in most oocytes from these donors were not detectable, or smaller than 15 nA, mRNA was extracted from the whole brains of 10 day postnatal rats and microinjected into the oocytes. IBa increased gradually during five days after mRNA injection. The maximum amplitude of the expressed voltage-activated barium current was usually larger than one hundred of nA on the third day after mRNA injection. In comparison, the expression of voltage-activated barium current was hardly detectable in oocytes injected by mRNA extracted from brains of embryonic rats. The voltage-dependence of activation and inactivation pharmacology of IBa were studied. It was found that IBa was inhibited potently by lanthanide cations (La+3,Nd+3,Sm+3,Eu+3,Gd+3,Dy+3,Er+3) at mumol/L concentration level. L-type calcium channel ligands, nifedipine and Bay K 8644 inhibited IBa at 100 mumol/L, while another dihydropyridine ligand (+/-) nimodipine enhanced IBa at the same concentration.

Cloning of a xylanase gene from the ruminal fungus Neocallimastix patriciarum 27 and its expression in Escherichia coli

An endo-beta-1,4-xylanase gene was cloned from Neocallimastix patriciarum 27 in the bacteriophage vector lambda gtWES lambda B and was subcloned into the plasmid vectors pUC18 and pUC19 in which xylanase activity was expressed in both orientations. The xylanase was located in the periplasmic space of the host, Escherichia coli HB101. The pH and temperature optima for periplasmic xylanase activity were 6.2 and 40 degrees C, respectively, and the Km for oat spelt xylan hydrolysis was 0.89 mg.mL-1. It also exhibited hydrolytic activity on carboxymethyl cellulose that was equivalent to 28% of the activity exhibited by the enzyme on xylan. It bound to crystalline cellulose, but lacked hydrolytic activity on amorphous cellulose. SDS-PAGE followed by zymogram analysis showed active bands of 68, 58, and 51 kDa. Isoelectric focusing in gels combined with zymogram analysis showed one band of xylanase activity with a pI of 3.6.

Protein conformational perturbations affect the photoreduction of native cytochrome c peroxidase (III) at alkaline pH

Ferric cytochrome c peroxidase (CCP) undergoes a ligation-state transition from a pentacoordinate, high-spin (5c/hs) heme to a hexacoordinate, low-spin (6c/1s) heme when titrated over a pH range of 7.30-9.70. This behavior is similar to that exhibited by the ferrous form of the enzyme. However, the photodissociation of the low-spin, axial ligand, exhibited by ferrous CCP at alkaline pH, is not observed for ferric CCP. Instead, a photoinduced reduction of the ferric heme is apparent in the pH range 7.90-9.70. In the absence of O2 and redox mediators such as methyl viologen (MV2+), the reoxidation of the photoreduced enzyme is very slow (tau 1/2 approximately 3 min). F(-)-bound CCP(III) (6c/hs) displays similar pH-dependent photoreduction. Horseradish peroxidase, however, does not. The formation of 6c/1s heme coincides with the onset of appreciable photoreduction (between laser pulses, > 60 ms) of CCP (III) at alkaline pH, suggesting a global protein conformational rearrangement within or around its heme pocket. Photoreduction of alkaline CCP(III) most likely involves intramolecular electron transfer (ET) from the aromatic residue in the proximal heme pocket to the photoexcited heme. We speculate that the kinetics of electron transfer are affected by changes in the orientation of Trp-191.

[The expression of kainate and GABA receptors in oocytes of Bufo bufo gargarizans]

Oocytes of Bufo bufo gargarizans were used as an expression system for analyzing structure of exogenous membrane protein and their functions. Poly (A)+ mRNA isolated from rat brain was injected into Toad (Bufo bufo gargarizans) oocytes (50 ng/oocyte). Rat brain kainic acid and gamma-aminobutyric acid(GABA) receptors expressed by the injected mRNA were integrated in the oocyte membrane 48 h after the injection at 19 degrees C. Membrane currents induced by kainic acid (5 x 10(-5) mol/L) and GABA (10(-4) mol/L) were 294.0 +/- 6.4 nA (n = 5) and 309.5 +/- 4.9 nA (n = 4) respectively. The kainic acid induced current reached its maximum value at about 10(-3) mol/L. Moreover, it was observed that the 36Cl- influx of the oocytes microinjected with mRNA was one-fold more rapid than the control oocytes. These results indicate that the oocytes of Bufo bufo gargarizans as those of Xenopus laevis can be used to express membrane proteins (receptors & transports) to acquire their proper functions from exogenous mRNA.

Effect of cobalt-60 irradiation on the infectivity of Paragonimus westermani metacercariae

A study was made to observe the effect of cobalt-60 irradiation on the viability of Paragonimus westermani metacercariae in Sinopotamon chekiangense crabs. The crabs were collected in mountain regions of the Zhejiang Province of China in which paragonimiasis is endemic. Adult cats and albino mice were infected with metacercariae irradiated at different doses. Dissection of the host animals was conducted 90 or 30 days, respectively, after infection for recovery of lung flukes. Anti-metacercariae antibody in infected mice was measured by enzyme-linked immunosorbent assay (ELISA). Results showed that metacercariae were unable to grow into adult worms in cats after exposure to gamma irradiation at a dose of 0.10 kGray. However, a small number of metacercariae exposed to a dose of 2.0 kGray excysted and survived in 1 mouse for 30 days. No worm was recovered from mice when the metacercariae were irradiated at a dose of 2.5 kGray. Seropositive results by ELISA were obtained when the mice were infected with metacercariae irradiated at doses ranging from 2.0 to 3.5 kGray.

[A voltage-dependent potassium channel of outward rectifier type in plasma membrane of oocyte from toad, Bufo bufo gargarizans]

Membrane properties of the fully-grown oocytes from toad, Bufo bufo gargarizans, were studied by using voltage-clamp technique. It was found that a sustained outward current was elicited by membrane depolarization to -30 mV or more positive value. The increase of the current was nearly proportional to the degree of depolarization. The peak value of the current ranged 2-5 microA at a membrane potential of 20 mV in oocytes from different toads. The current was inhibited by antagonists of potassium channel, TEA and 4-AP. The concentration of TEA capable of inhibiting half of the current was 2.6 mmol/L. Chloride channel antagonist 9-AC (2.5 mmol/L) had no effect on the current. Triple the extracellular calcium concentration did not show any effect either. The reversal potential of the current varied with an increase of 47.3 mV per decade change of the extracellular potassium concentration. Changing extracellular concentration of sodium or chloride did not shift the reversal potential. It was concluded that the outward current was a voltage-activated potassium current. The voltage-dependent potassium current decreased after treatment of the oocytes with progesterone to a state of maturation. A large decrease of the current (to about 1/20 of the control) occurred to the oocytes obtained from hibernating toads while a less striking decrease of the current (to about 1/3 of the control) was observed in the oocytes from toads all year round reared at 25-30 degrees C.

Wild-type p53 activates transcription in vitro

The p53 protein is an important determinant in human cancer and regulates the growth of cells in culture. It is known to be a sequence-specific DNA-binding protein with a powerful activation domain, but it has not been established whether it regulates transcription directly. Here we show that intact purified wild-type human and murine p53 proteins strongly activate transcription in vitro. This activation depends on the ability of p53 to bind to a template bearing a p53-binding sequence. By contrast, tumour-derived mutant p53 proteins cannot activate transcription from the template at all, and when complexed to wild-type p53, these mutants block transcriptional activation by the wild-type protein. Moreover, the simian virus 40 large T antigen inhibits wild-type p53 from activating transcription. Our results support a model in which p53 directly activates transcription but this activity can be inhibited by mutant p53 and SV40 large T antigen through interaction with wild-type p53.

Identification of a coactivator that increases activation of transcription by serum response factor and GAL4-VP16 in vitro

We have identified an activity in HeLa cell nuclear extracts that increases activation of transcription in vitro by serum response factor (SRF). This coactivator activity, termed CoS, did not affect basal (TATA only) transcription. CoS initially fractionated with transcription factors TFIIE and -F but was further purified to separate it from both TFIIE and -F as well as any other general transcription factor activity. We found that CoS was not specific for SRF activation, since it also increased transcriptional activation by the chimeric GAL4-VP16 activator. Differences among CoS and recently identified coactivators are discussed.

Yeast flavohemoglobin is an ancient protein related to globins and a reductase family

The hemoglobin of yeast is a two-domain protein with both heme and flavin prosthetic groups. The nucleotide sequences of the cDNA and genomic DNA encoding the protein from Saccharomyces cerevisiae show that introns are absent and that both domains are homologous with a flavoheme protein from Escherichia coli. The heme domains are also homologous with those of O2-binding heme proteins from several other distantly related bacteria, plants, and animals; all appear to be members of the same globin superfamily. Although the homologous hemoglobin of the bacterium Vitreoscilla sp. is a single-domain protein, several bacteria have related O2-binding heme proteins whose second domains have different structures and enzymatic activities: dihydropteridine reductase (E. coli), cytochrome c reductase (Alcaligenes eutrophus), and kinase in the O2 sensor of Rhizobium meliloti. This indicates that one evolutionary pathway of hemoglobin is that of a multipurpose domain attached to a variety of unrelated proteins to form molecules with different functions. The flavin domain of yeast hemoglobin is homologous with members of a flavoprotein family that includes ferredoxin reductase, nitric oxide synthase, and cytochrome P-450 reductase. The correspondence of yeast and E. coli flavohemoglobins indicates that the two-domain protein has been conserved intact for as long as 1.8 billion years, the estimated time of divergence of prokaryotes and eukaryotes provided that cross-species gene transfer has not occurred.

A ubiquitous factor (HF-1a) and a distinct muscle factor (HF-1b/MEF-2) form an E-box-independent pathway for cardiac muscle gene expression

Recent studies have identified a conserved 28-bp element (HF-1) within the rat cardiac MLC-2 gene which confers cardiac muscle-specific and inducible expression during myocardial cell hypertrophy. Utilizing a combination of independent experimental approaches, this study characterizes two cardiac nuclear factors which bind to HF-1, a ubiquitous factor (HF-1a), and an A + T-rich binding factor (HF-1b) which is preferentially expressed in differentiated cardiac and skeletal muscle cells. The HF-1a binding site is located in a core region of the 28-bp conserved element, immediately upstream from the A + T-rich HF-1b site, which is homologous to the MEF-2 site found in a number of muscle genes. By a number of separate criteria (gel mobility shift, competition, and mutagenesis studies), HF-1b and MEF-2 appear to be indistinguishable and thus are either identical or closely related muscle factors. Transient assays of luciferase reporter genes containing point mutations throughout the 28-bp HF-1 regulatory element document the importance of both the HF-1a and HF-1b sites in transient assays in ventricular muscle cells. In the native 250-bp MLC-2 promoter fragment, mutations in the single E box had little effect on cardiac muscle specificity, while point mutations in either the HF-1a or HF-1b binding site significantly reduced promoter activity, underscoring the importance of both the HF-1a and HF-1b sites in the transcriptional activation of this cardiac muscle gene. Thus, this study provides evidence that a novel, ubiquitous factor (HF-1a) and a muscle factor (HF-1b/MEF-2) can form a novel, E-box-independent pathway for muscle-specific expression in ventricular cardiac muscle cells.

Studies on the use of cobalt-60 gamma irradiation to control infectivity of Clonorchis sinensis metacercariae

The purpose of the present study was to observe the survival and development of Clonorchis sinensis metacercariae in their final hosts after Cobalt-60 gamma irradiation of isolated metacercariae or the parasite in fish. Guinea pigs or albino rats were orally infected with irradiated metacercariae by gavage. Bioassay, fecal examination for ova, and necropsy of infected animals, were the methods used for the estimation of minimum effective dose of gamma irradiation to control infectivity of the metacercariae. Results showed that the minimum effective irradiation dose for isolated metacercariae was 0.05 kGy. The LD50 of the irradiation dose for metacercariae in fish was 0.05 kGy, and the minimum effective dose was 0.15 kGy. No significant difference in radiation susceptibility to Co-60 gamma irradiation was found among C. sinensis metacercariae in fishes collected at different localities in northern, middle or southern parts of China. The present finding suggests that irradiation of fish by 0.15 kGy could control infectivity of C. Sinensis metacercariae and thus be adopted as a control measure in preventing infections.

In vitro squelching of activated transcription by serum response factor: evidence for a common coactivator used by multiple transcriptional activators

Low amounts of serum response factor (SRF) activate transcription in vitro from a fos promoter construct containing an SRF binding site. Using this human HeLa cell-derived in vitro transcription system, we have found that high amounts of SRF inhibited, or 'squelched', transcription from this construct. Transcription from several other promoters activated by different gene-specific factors, including CREB and the acidic activator VP16, was also inhibited by high amounts of SRF. Basal transcription, from TATA-only promoters, however, was not inhibited. These results suggest that SRF binds to a common factor(s) (termed coactivator) required for activated transcription by a diverse group of transcriptional activators. Inhibition of transcription by SRF could be blocked by a double stranded oligonucleotide containing an SRF binding site. Mutations in SRF which abolished its DNA binding activity also reduced its ability to inhibit transcription. In addition, a C-terminal truncation of SRF which reduced its ability to activate transcription also reduced SRF's ability to inhibit transcription. These results suggest that activation and inhibition of transcription may be mediated by SRF binding to the same factor and that SRF can only bind to this factor when SRF is bound to plasmid DNA.

pH fluctuations versus reflux episodes in patients with gastroesophageal reflux disease: their optimal thresholds and significance in diagnosis

In physiological and pathological conditions, pH monitoring in the esophagus shows small variations as well as more pronounced deflections. However, only the latter are traditionally taken into account in 24-hour pH monitoring analysis. The present study was designed to establish optimal thresholds of pH fluctuations versus reflux episodes in separating physiological and pathological gastroesophageal reflux (GER) and to evaluate their significance in the diagnosis. Twenty-four-hour intraesophageal pH monitoring and endoscopy were performed in 62 patients with GER symptoms and in 42 healthy controls. The results showed that the percentages of the time with pH fluctuations in patients with and without esophagitis and in healthy controls were, on average, 12.65, 9.5 and 2.76% in 24 h, respectively, and the respective percentages of the time with reflux episodes in the same groups in 24 h were, on average, 3.12, 2.04 and 0.18%, respectively. Using a receiver-operating-characteristic curve analysis, less than 6.7% of the time with pH fluctuations and less than 0.1% of the time with reflux episodes were defined as the combined thresholds for physiological versus pathological reflux. The sensitivity of the combined thresholds for the detection of GER patients with and without esophagitis was 96.7 and 90%, respectively, and their specificity for the diagnosis of patients with abnormal GER was 100%. It is concluded that pH fluctuations and reflux episodes, when evaluated together, are more useful for classifying patients with GER and their combined thresholds yield higher diagnostic accuracy in assessing patients with gastroesophageal disease.

Polarized distribution of coated pits and coated vesicles in the rat lens: an electron microscopy and WGA-HRP tracer study

The presence and distribution of coated pits (CPs) and coated vesicles (CVs) in the rat lens were studied by thin-section electron microscopy (TEM) and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) as a tracer. TEM revealed that CPs and CVs were approximately 150 nm in diameter, of which the characteristic clathrin coat was approximately 20 nm thick. CPs and CVs were found in both epithelium and superficial fiber cells of the entire lens, and were distributed preferentially along the basal membrane facing the lens capsule. It was estimated that more than 80% of CPs and CVs in the entire epithelium were seen along the basal membrane. The number of CPs and CVs along the basal membrane in the equatorial epithelium (4.4 per 10 microns membrane) was similar to that at the central zone (3.8 per 10 microns membrane), but there was a significant increase along the apical and lateral surfaces of the equatorial epithelium compared to that of the central epithelium, although the overall number was considerably smaller. In the lens fibers, CPs and CVs were usually found within 2-3 superficial layers of fiber cells. The number of CPs and CVs along the basal membrane of young fibers at the post-equatorial region (3.1 per 10 microns membrane) was 3-fold greater than that of the mature fibers at the posterior polar area (1 per 10 microns membrane). Thus, CPs and CVs along the entire basal membrane showed a gradual decrease in number from the anterior (and equatorial) regions to the posterior polar surface of the lens. WGA-HRP experiments showed that approximately 80% of tracer-carrying pits and vesicles were also found along the basal surface of the equatorial epithelium. This study suggests that a polarized distribution of CPs and CVs along the basal surface of epithelium and superficial fiber cells may facilitate receptor-mediated endocytosis of important macromolecules directly from the aqueous humor and vitreous body into metabolically active lens cells.

Regulation of cardiac gene expression during myocardial growth and hypertrophy: molecular studies of an adaptive physiologic response

Studies from both in vivo and in vitro model systems have provided an initial skeleton of the potential signaling pathways that might regulate cardiac genes during growth and hypertrophy. One of the first detectable changes in cardiac gene expression is the activation of a program of immediate early gene expression, which is distinct for the hypertrophic response, and is conserved in multiple models of both in vivo and in vitro hypertrophy. Diverse and distinct hormonal stimuli have been documented to activate several features of the hypertrophic response, including several autocrine and paracrine factors. Although the signaling mechanisms that link these factors with the activation of cardiac gene expression are unclear, recent studies suggest that the activation of protein kinase C may represent one of the most proximal common events in this signaling cascade. The activation of cardiac target genes induces a program of embryonic gene expression, including the atrial natriuretic factor (ANF) gene. The cis sequences that mediate cardiac-specific and inducible expression of an embryonic marker gene (ANF) can be segregated by studies in both cultured cell models and in vivo models of hypertrophy in transgenic mice, suggesting that specific sets of regulatory elements may exist for inducible expression of this class of cardiac gene responses. However, the induction of a constitutively expressed contractile protein gene (MLC-2) is mediated by a set of conserved elements that regulate both cardiac-specific and inducible expression. Finally, a subset of cardiac muscle genes appears to be noninducible during in vivo or in vitro hypertrophy in myocardial cells, demonstrating specificity of transcriptional activation during the hypertrophic process. The development of a bona fide in vivo pressure overload model of hypertrophy in a small animal model that can be genetically manipulated, such as the in vivo murine model recently described, should allow a rigorous analysis of the role of these specific signaling mechanisms in the activation of the responses of cardiac genes during the hypertrophic process in vivo.

Diazemuls versus diazepam as premedication in upper gastrointestinal endoscopy: a randomised cross-over study

The efficacy and tolerability of Diazemuls versus conventional diazepam as endoscopic premedication was evaluated in a study with a cross-over design performed in 26 patients undergoing upper gastrointestinal tract endoscopy. No statistically significant differences were found between the two forms of premedication with regard to degree of sedation, patient compliance or recovery of psychomotor function. With respect to short-term amnesic effects, efficacy and tolerability Diazemuls was comparable to the conventional formulation of diazepam. Diazemuls may therefore be proposed as an alternative premedication for endoscopy.

[A distinct centro-peripheral gradient of development in dopaminergic amacrine cells of cat retina]

The centro-peripheral gradient of development in dopaminergic (DA) amacrine cells of cat retina has been studied by TH immunocytochemical method. Type I of TH immunoreactive neurons is typical DA cell. They reveal a clear centro-peripheral gradient of differentiation and maturation in space and time course during postnatal development. (1) At P1 stage, the TH I cells vary in TH immunoreactivity, soma sizes and dendritic maturation. Responding to degree of development, they can be divided into I1, I2 and I3. The more differentiated I1 cells, larger and darkly immuno-stained stellate cells mostly concentrates at central retina, while the less differentiated I3 cells, smaller and lightly immunostained irregular cells concentrate at peripheral retina. I2 cells of moderate differentiation distribute over all the retina. (2) During the postnatal development, from P1 to P13, the dense area of the TH I1 cells spreads peripherally in company with the increase of the total number of TH I1 cells, comprising the central 30% of the retina at P1, 65% at P6 and almost the whole of the retina by P13. After eye opening, as the TH I cells have spread at far peripheral region, the differences in soma diameters and dendritic maturation of TH I cells between central and peripheral retina decrease gradually and the centro-peripheral gradient of maturity of TH I cells becomes less distinct. At P23, no significant difference is visible in either soma diameter or dendritic maturation in these two areas: thus, the centro-peripheral gradient is no longer apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum response factor affects preinitiation complex formation by TFIID in vitro

Serum response factor (SRF), a transcription factor that binds to the serum response element (SRE) of the c-fos proto-oncogene, activates transcription of an SRE-containing reporter plasmid in vitro. We describe here preincubation experiments which indicate that SRF activates transcription by facilitating the formation of active preinitiation complexes. Full activation by SRF occurred if SRF was preincubated with the general transcription factors. However, if the general transcription factors were preincubated and SRF was added subsequently, only poor activation of transcription was observed. This suggests that SRF must be present during preinitiation complex formation and that this complex is refractory to activation if SRF is absent during its formation. We have fractionated the general transcription factors and found that only a highly purified fraction containing the TATA-binding factor TFIID (and other unidentified components) must be present during preincubation for maximal transcriptional induction by SRF. This supports a model in which SRF activates transcription by affecting the conformation of TFIID bound to the promoter. Also of interest was the finding that recombinant human TFIID expressed in bacteria cannot mediate SRF-activated transcription, although it does support basal transcription. These results suggest that SRF may affect TFIID via a cofactor or coactivator.

[Reflux esophagitis: therapy with H2-blockers, and motility disorders]

In order to investigate the response of gastroesophageal reflux after medically induced healing of esophagitis and its relation to the occurrence of relapse during prophylactic treatment, 20 patients with erosive/ulcerative esophagitis underwent 24 hour esophageal pH monitoring before and after healing achieved with 12 to 24 weeks with ranitidine 150 or 300 mg bd. Compared with pretreatment values, after macroscopic healing, a significant reduction in daytime median percentage of reflux time and median number of reflux episodes lasting more than 5 min were observed, whereas during the night time reflux frequency and severity did not change. During maintenance treatment with ranitidine at half the acute dosage five of the six patients who had shown no improvement in gastroesophageal reflux after acute healing, relapsed. These results suggest that, in contrast to previous work, a decrease in gastroesophageal reflux in patients with reflux esophagitis can be achieved after macroscopic healing obtained with H2-antagonists, and that the occurrence of such a reduction after acute healing is predictive of a good response to long-term treatment.

[Gas chromatograms of fatty acids from Rickettsia and their similarities]

Fatty acid compositions of 7 strains of Rickettsia were analyzed by a on-line GC/MS system. These strains were R. prowazekii E, R. conorii Simko, R. rickettsii R, R. sibirica Barbash and 246, R. sinkiangensis Jinghe, and R. heilungkiangensis 54. The samples were purified by means of the concentrated salt-ether method. There were about 50 peaks in the fatty acid profiles, and 16 of these peaks were determined, i.e. C22:0, C19:0, C18:0, C18:1, C18:2, C17:0, C16:0, C16:1, 3-OH-C14:0, C15:0, C14:0, C13:0, 2-OH-C12:0, C12:0, 2-OH-C10:0, and C11:0. The major fatty acids were the saturated straight chain acids (e.g. C16:0, C18:0, C14:0) and the unsaturated straight chain acids (e.g. C18:1, C18:2, C16:1). Similarities of fatty acid profiles of tested strains were discriminated by the improved Kulik-Vincent method. The result showed that the KV's coefficient of strains Jinghe and 246 was 97.0%, and the KV's coefficient of strains 54 and the others was 81.6-94.6%.

A conserved 28-base-pair element (HF-1) in the rat cardiac myosin light-chain-2 gene confers cardiac-specific and alpha-adrenergic-inducible expression in cultured neonatal rat myocardial cells

To study the transcriptional regulatory mechanisms which mediate cardiac-specific and inducible expression during myocardial cell hypertrophy, we have extensively characterized the rat cardiac myosin light-chain-2 (MLC-2) gene as a model system. The MLC-2 gene encodes a relatively abundant contractile protein in slow skeletal and cardiac muscle and is upregulated during in vivo cardiac hypertrophy and alpha-adrenergic-mediated hypertrophy of neonatal rat myocardial cells. In transient expression assays employing a series of MLC-2-luciferase constructs, recent studies have identified a 250-bp fragment which is sufficient for both cardiac-specific and alpha-adrenergic-inducible expression. Within this 250-bp fragment lie three regions (HF-1, HF-2, and HF-3), each greater than 10 bp in length, which are conserved between the chicken and rat cardiac MLC-2 genes, suggesting their potential role in the regulated expression of this contractile protein gene. As assessed by substitution mutations within each of the conserved regions, the present study demonstrates that HF-1 and HF-2 are important in both cardiac-specific and inducible expression, while HF-3 has no detectable role in the regulated expression of the MLC-2 gene in transient expression assays. HF-1 sequences confer both cardiac-specific and inducible expression to a neutral promoter-luciferase construct but have no significant effect in the skeletal muscle or nonmuscle cell contexts. Thus, these studies have identified a new cardiac-specific regulatory element (HF-1) which plays a role in both cardiac-specific and inducible expression during myocardial cell hypertrophy.

Mutational analysis of the functional domains of yeast K1 killer toxin

To determine the functional domains of K1 killer toxin, we analyzed the phenotypes of a set of mutations throughout regions encoding the alpha- and beta-toxin subunits that allow secretion of mutant toxins. A range of techniques have been used to examine the ability of mutant toxins to bind to beta-glucan cell wall receptor and to form lethal ion channels. Our results indicate that both the alpha and beta subunits are involved in beta-glucan receptor binding. Defects in ion channel formation and toxin immunity are confined to the hydrophobic alpha subunit of the toxin.