Probing novel elements for protein splicing in the yeast Vma1 protozyme: a study of replacement mutagenesis and intragenic suppression

Protein splicing is a compelling chemical reaction in which two proteins are produced posttranslationally from a single precursor polypeptide by excision of the internal protein segment and ligation of the flanking regions. This unique autocatalytic reaction was first discovered in the yeast Vma1p protozyme where the 50-kD site-specific endonuclease (VDE) is excised from the 120-kD precursor containing the N- and G-terminal regions of the catalytic subunit of the vacuolar H(+)-ATPase. In this work, we randomized the conserved valine triplet residues three amino acids upstream of the C-terminal splicing junction in the Vma1 protozyme and found that these site-specific random mutations interfere with normal protein splicing to different extents. Intragenic suppressor analysis has revealed that this particular hydrophobic triplet preceding the C-terminal splicing junction genetically interacts with three hydrophobic residues preceding the N-terminal splicing junction. This is the first evidence showing that the N-terminal portion of the V-ATPase subunit is involved in protein splicing. Our genetic evidence is consistent with a structural model that correctly aligns two parallel beta-strands ascribed to the triplets. This model delineates spatial interactions between the two conserved regions both residing upstream of the splicing junctions.

Ultrasonographic assessment of regional differences in atherosclerotic lesions in patients with hypertension, diabetes mellitus, or both

We evaluated risk factors involved in regional differences in atherosclerotic lesions in patients with hypertension, diabetes mellitus, or both. Using ultrasonography, we examined the brachial, common carotid, and common femoral arteries in 65 hospitalized Japanese patients (15 controls, 18 patients with hypertension, 16 with diabetes mellitus, and 16 with both hypertension and diabetes mellitus). They ranged in age from 39 to 81 yr, mean 60.3 yr. The thickness of the intima-media complex of the far wall was measured, and the severity of atherosclerotic plaques was graded according to maximal lumen stenosis. The intima-media thickness in the carotid and femoral arteries was significantly greater in the hypertensive patients and the hypertensive patients with diabetes than in the controls. Severity of plaque was greater in the hypertensive patients with diabetes than in the controls. Plaque grades were higher in the carotid and femoral arteries than in the brachial artery. Multiple regression analysis revealed that age and mean blood pressure were strongly associated with the intima-media thickness in all three arteries. In the femoral artery, cigarette smoking and hyperglycemia also significantly correlated with the intima-media thickness. Plaque grades increased with age in the carotid and brachial arteries, while in the femoral artery the grade increased with cigarette smoking and serum cholesterol concentration. These findings suggest that the extent of atherosclerosis and its underlying risk factors differ among arterial sites. In addition, risk factors may partly differ according to the stage of atherosclerosis. To prevent or reverse atherosclerosis, the above differences should be taken into account.

Protein splicing in the yeast Vma1 protozyme: evidence for an intramolecular reaction

Protein splicing is an autocatalytic reaction of a single polypeptide in which a spliced intervening sequence is excised out and the two external regions are ligated with the peptide bond to yield two mature proteins. We examined the reaction mechanism using a folding-dependent in vitro protein splicing system. Protein splicing proceeds at an optimal pH of 7 and is an intramolecular reaction. The reaction is not inhibited by potential protease inhibitors, suggesting that its mechanism is different from those catalyzed by known proteases.

Percutaneous transluminal angioplasty attenuates day-night difference in ambulatory blood pressure in renovascular hypertension

To evaluate whether the circadian rhythm of blood pressure (BP) was altered in renovascular hypertension (RVH), ambulatory BP was monitored using a noninvasive recorder in nine patients with RVH attributable to fibromuscular dysplasia before and after percutaneous transluminal angioplasty (PCTA). The circadian rhythm of BP was assessed by the day-night difference in BP and by the single cosinor method. The day-night difference in BP before PCTA was significantly greater than in age- and sex-matched normotensive subjects (n = 9, P < .01) and patients with essential hypertension (n = 9, P < .05). PCTA decreased significantly the 24-h BP as well as plasma renin activity (P < .01). In the chronogram, the BP reduction after PCTA was evident especially during the day. Accordingly, the day-night difference in BP decreased significantly after PCTA (P < .01). In the cosinor analysis, the mesor and the percent amplitude of BP decreased significantly after PCTA (P < .01). In summary, circadian rhythm of BP was preserved or rather exaggerated in RVH. The stimulated renin angiotensin system in RVH possibly contributes to the altered circadian rhythm of BP primarily by elevating the daytime BP.

Effects of CP-060S on membrane channels in vascular smooth muscle cells from guinea pig

The newly developed cardioprotective drug, CP-060S, (-)-(S)-2-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]-3-[3-[N-methyl-N- [2-(3,4-methylenedioxyphenoxy) ethyl] amino] propyl]-1,3-thiazolidin-4-one hydrogen fumarate, is reported to possess a vasodilating action. Our objective was to examine the effects of CP-060S on the membrane channels in mesenteric arterial cells from guinea pigs, using whole-cell patch-clamp techniques. CP-060S inhibited the Ca2+ channel current in a concentration-dependent manner (ED50 = 1.7 microM at a holding potential of -80 mV and a stimulation frequency of 0.1 Hz). The inhibition was potentiated by a more depolarized holding potential and a higher stimulation frequency. These effects of CP-060S resembled those of diltiazem and gallopamil more than to those of nifedipine; the inhibition was more frequency dependent and less holding-potential dependent than with nifedipine. Higher concentrations of CP-060S also inhibited the delayed K+ channel currents (ED50 = 18 microM). The present observations suggest that CP-060S exhibits the profile of a Ca2+ channel antagonist, similar to that of diltiazem and gallopamil.

Applications of the long and accurate polymerase chain reaction method in yeast molecular biology: direct sequencing of the amplified DNA and its introduction into yeast

A DNA fragment longer than 10 kb can be amplified by the long and accurate polymerase chain reaction (LA-PCR) method. We demonstrate here applications of this technique in molecular biological studies of Saccharomyces cerevisiae. We have shown that DNA fragments amplified by LA-PCR can be directly used as a template in the chain-termination sequencing protocol, making it possible to quickly identify the DNA insert of yeast genomic library clones. We have also shown that the amplified yeast DNA can easily be introduced into yeast by co-transformation with linearized vector DNA. Overlapping DNA between the amplified yeast fragment and the vector must be more than 20 bp long in order to obtain 90% or more correct recombinant plasmids. These results suggest that simple amplification of yeast clones by LA-PCR can replace the previous procedures of yeast clone recovery, consisting of transformation of Escherichia coli, propagation of plasmids in E. coli and preparation of plasmid DNA.

Identification of three core regions essential for protein splicing of the yeast Vma1 protozyme. A random mutagenesis study of the entire Vma1-derived endonuclease sequence

The translation product of the VMA1 gene of Saccharomyces cerevisiae undergoes protein splicing, in which the intervening region is autocatalytically excised and the franking regions are ligated. The splicing reaction is catalyzed essentially by the in-frame insert, VMA1-derived endonuclease (VDE), which is a site-specific endonuclease to mediate gene homing. Previous mutational analysis of the splicing reaction has been concentrated extensively upon the splice junctions. However, it still remains unknown which amino acid residues are crucial for the splicing reaction within the entire region of VDE and its neighboring elements. In this work, a polymerase chain reaction-based random mutagenesis strategy was used to identify such residues throughout the overall intervening sequence of the VMA1 gene. Splicing-defective mutant proteins were initially screened using a bacterial expression system and then analyzed further in yeast cells. Mutations were mapped at the N- and C-terminal splice junctions and around the N-terminal one-third of VDE. We identified four potent mutants that yielded aberrant products with molecular masses of 200, 90, and 80 kDa. We suggest that the conserved His362, newly identified as the essential residue for the splicing reaction, contributes to the first cleavage at the N-terminal junction, whereas His736 assists the second cleavage by Asn cyclization at the C-terminal junction. Mutations in these regions did not appear to destroy the endonuclease activity of VDE.

Stretch-activated whole-cell currents in smooth muscle cells from mesenteric resistance artery of guinea-pig

1. Stretch-activated (SA) channels were studied in smooth muscle cells isolated from mesenteric resistance arteries using the whole-cell patch-clamp method. Membrane stretch was achieved by cell inflation after application of positive pressure through a patch electrode. 2. In the voltage-clamp configuration, cell inflation increased and cell deflation decreased the membrane conductance. Conductance of the evoked current depended on the increase in cross-sectional area of the cell. The current-voltage relationship was linear between -80 and 0 mV, while further hyperpolarization showed a slight inward rectification. 3. The reversal potential of the SA current depended on the extracellular Na+ concentration, suggesting that the inward SA current was carried predominantly by Na+. The SA current was also carried by other cations, suggesting that the channel responsible for this current is a non-selective cation channel. The permeability sequence of cations as assessed by reversal potential was as follows: K+ > or = CS+ > or = Na+ > Li+. The channel was also permeable to Ca2+. 4. Extracellular Ca2+ and Gd3+ inhibited the SA current carried by monovalent cations in a concentration-dependent manner with IC50 (concentration giving 50% of maximal inhibition) values of 0.9 mM and 14 microM, respectively. 5. In the current-clamp configuration, membrane stretch depolarized the cell, and 100 microM Gd3+ inhibited the stretch-induced depolarization. 6. The results suggest that SA cation channels exist in arterial smooth muscle cells. Activation of the channels may modify membrane potential and intracellular ionic environment, and promote stretch-mediated cell responses.

Molecular cloning and characterization of Drosophila genes encoding small GTPases of the rab and rho families

We have isolated eight genes from Drosophila, small GTPases. They can be classified into three rab family genes (Drab2, Drab5, Drab11) and five rho family genes (Drac1a, Drac1b, Drac3, Dcdc42, DrhoA). While Drac3 is a novel type of rac gene, others are homologues of known mammalian genes for small GTPases. Northern blot analyses showed that all the genes are expressed throughout all developmental stages from embryo to adult. In situ hybridization to embryos revealed that Drab2, Drac1b, and Drac3 are highly expressed in the nervous system, in the trunk mesoderm, and in the cephalic mesoderm, respectively. Since hemocytes are derived from the cephalic mesoderm, we carried out double stainings using a hemocyte marker anti-peroxidasin antibody and Drac3 in situ hybridization. We found that Drac3 is expressed in hemocyte precursor cells. In the Drac3 deficiency embryos, the hemocyte precursor cells start to differentiate normally, but never develop into mature hemocytes, indicating that Drac3 is essential for their maturation. The DrhoA and Dcdc42 genes complemented S. cerevisiae rho1 and cdc42 mutations in the same manner as human rhoA and CDC42, respectively. These results suggest functional similarity between Drosophila and mammalian small GTPase genes.

Enhanced electrical activity in mesenteric arteries from salt-loaded Dahl salt-sensitive rats: actions of prostaglandin H2 on membrane channels

Salt loading increases blood pressure in Dahl salt-sensitive (Dahl S) rats. We have previously shown that the mesenteric artery of salt-loaded Dahl S rats exhibits enhanced electrical activity that is corrected by a cycloxygenase inhibitor, indomethacin. Prostaglandin H2 (PGH2) is a product of cycloxygenase that is known as an intrinsic vasoconstricting factor in spontaneously hypertensive rats. Our hypothesis is that tissue production of PGH2 would be involved in the enhanced electrical activity of arteries from salt-loaded Dahl S rats. In the present study, to clarify this possibility, we evaluated the actions of PGH2 on membrane channels in arterial cells from Dahl S rats. Membrane currents were recorded by whole-cell voltage clamp technique in single smooth muscle cells from the mesenteric artery. Application of PGH2 evoked an inward current that was mainly dependent on extracellular Na+ in the physiological extracellular solution. When high Ba2+ solution was used for the extracellular solution, PGH2 also evoked the inward current, suggesting that a divalent cation, such as Ba2+ or Ca2+, could permeate the PGH2-activated channels. In contrast, the L-type Ca2+ channel currents were not enhanced by the application of PGH2. The present results suggest that production of PGH2 contributes to the enhanced electrical activity by activating cation-permeable channels and depolarizing the membrane potential. PGH2 also directly stimulates the Ca2+ influx by activating Ca2+ permeable channels.

Fatal GVHD demonstrating an involvement of respiratory muscle following donor leukocyte transfusion (DLT)

A 41-year-old female patient with AML, who relapsed after an allogeneic BMT from her HLA-identical sister, was treated by a donor leukocyte transfusion (DLT). Thereafter, bone marrow aplasia accompanied by the disappearance of leukemic blasts following the GVHD was observed. The patient died of chronic GVHD with respiratory muscle involvement 19 months after the DLT. Although the DLT was considered helpful in suppressing the proliferation of the leukemic cells, it might also have caused the severe GVHD observed in this case. Efforts to separate the lymphocyte clones responsible for GVL from those for the GVHD thus appear to be necessary for the further development of the therapeutic approach, so-called DLT.

Role of eicosanoids in alteration of membrane electrical properties in isolated mesenteric arteries of salt-loaded, Dahl salt-sensitive rats

1. The role of eicosanoids in altered membrane electrical properties of Dahl salt-sensitive (DS) rats was investigated, by use of conventional microelectrodes technique, in isolated superior mesenteric arteries of DS rats and Dahl salt-resistant (DR) rats fed either a high or low salt diet. 2. The membrane was significantly depolarized in salt-loaded DS rats compared with the other three groups. In addition, the arteries of salt-loaded DS rats exhibited spontaneous electrical activity. 3. Spontaneous electrical activity in salt-loaded DS rats was inhibited by the following: indomethacin, a cyclo-oxygenase inhibitor; ONO-3708, a prostaglandin H2/thromboxane A2 receptor antagonist; OKY-046, a thromboxane A2 synthase inhibitor; nicardipine, a Ca(2+)-channel antagonist and by Ca(2+)-free solution. In addition, spontaneous electrical activity was enhanced by a thromboxane A2 analogue and by prostaglandin H2. Spontaneous electrical activity was unaffected by phentolamine, atropine and tetrodotoxin. 4. Membrane potential in arteries of salt-loaded DS rats was not affected by either indomethacin or ONO-3708. 5. Spontaneous contraction, sensitive to indomethacin, was present, and contractile sensitivity to high potassium solution was enhanced in arteries of salt-loaded DS rats. 6. These findings suggest that eicosanoid action, together with membrane depolarization, may lead to the activation of voltage-dependent Ca(2+)-channels, thereby causing spontaneous electrical activity in mesenteric arteries of salt-loaded DS rats. In addition, tension data suggest that these changes in membrane properties are related to enhanced contractile activities in salt-loaded DS rats. Mechanisms of depolarization remain to be determined.

Ambulatory blood pressure monitoring in patients with essential hypertension treated with a new calcium antagonist, cilnidipine

Cilnidipine (FRC-8653), a new dihydropyridine calcium antagonist, was given to 14 hospitalized patients with essential hypertension, and 24-hour ambulatory blood pressure (BP) monitoring was performed. Once-daily administration of cilnidipine (5-20 mg) for 1-3 weeks decreased the 24-hour average BP significantly from 149 +/- 4/88 +/- 2 mmHg to 141 +/- 3/82 +/- 2 mmHg without any change in the pulse rate. The decrease in ambulatory BP by cilnidipine was evident during the daytime (156 +/- 4/93 +/- 2 mmHg to 143 +/- 5/84 +/- 2 mmHg, p < 0.01 for systolic BP and p < 0.01 for diastolic BP), while it was mild during nighttime (141 +/- 4/80 +/- 2 mmHg to 133 +/- 4/76 +/- 3 mmHg, p < 0.05 for systolic and ns for diastolic BP). The decrease in the ambulatory BP over the whole day and during the nighttime was significantly correlated with the basal ambulatory BP levels. When the subjects were divided into the high ambulatory BP (n = 7) and low ambulatory BP (n = 7) groups, the BP reduction by cilnidipine was evident throughout 24 hours in the high ambulatory BP group, while it was mild and significant only during daytime in the low ambulatory BP group. In summary, once-daily cilnidipine exerts a sufficient and prolonged reduction of BP without an increase in the pulse rate in patients with hypertension. The potency of cilnidipine to decrease ambulatory BP may depend on the basal ambulatory BP level. Cilnidipine is thus a useful antihypertensive drug that may not cause an excessive decrease in BP or a reflex tachycardia.

Association between hyperinsulinemia and intima-media thickness of the carotid artery in normotensive men

OBJECTIVES

To determine whether hyperinsulinemia is associated with early atherosclerosis in normotensive men of a work site population.

DESIGN AND METHODS

Six hundred and seventeen subjects were screened from 8678 male transport workers for the further examination of cardiovascular disease and diabetes. Subjects aged less than 40 years, those with hypertension or diabetes, or both, and those being administered medications for hyperlipidemia were excluded. Finally, 164 normotensive, nondiabetic subjects were enrolled. The intima-media thickness (IMT) was measured by B-mode ultrasonography with a 7.5 MHz probe. Electrocardiography, a 75 g oral glucose-tolerance test (OGTT) and blood chemistry measurements were also performed. The sum of insulin values (sigmaIRI) and the ratio of the sum of insulin values to blood glucose levels (sigmaIRI/sigmaBG) in the 75 g OGTT were used as markers of hyperinsulinemia.

RESULTS

The mean age of the subjects was 52 +/- 5 years (mean +/- SD). In a univariate analysis, IMT was associated with age, systolic blood pressure, body mass index, sigmaIRI, and sigmaIRI/sigmaBG. Multivariate analysis showed that age, total cholesterol, and sigmaIRI (or sigmaIRI/sigmaBG) were independent risk factors for IMT.

CONCLUSIONS

These results suggest that, in addition to age and total cholesterol, hyperinsulinemia as assessed by an OGTT is associated with early atherosclerosis in normotensive, nondiabetic men of a work site population.

Effect of dimerization of the D-glucose analogue of muramyl dipeptide on stimulation of macrophage-like cells

N-Acetylmuramyl-L-alanyl-D-isoglutamine (MDP) is the minimum required structure responsible for the immunoadjuvant activity of the bacterial cell wall. The D-glucose analogue of MDP (GADP) was reported to show a higher immunoadjuvant activity than MDP itself. Although the mechanism of activation by MDP and the existence of receptor against MDP are not clear, the patch formation and cluster formation of receptors are important steps on the signal transduction by such bioactive molecules. It is expected that the cluster effect such as antennary oligosaccharides reported by Lee et al. increased the affinity of ligand against receptor and accelerated the patch formation and cluster formation of receptors. In order to discuss the effect of multivalent-ligand formation of GADP on the activation of immunocompetent cells in more detail, we have synthesized GADP dimers combined through various lengths of alkyl and poly(ethylene glycol) (PEG) spacer groups as the simple models of multivalent-ligand molecule of GADP and evaluated their immunological enhancement activities in vitro. The GADP dimers showed a higher level stimulatory activities against macrophage-like cells than free GADP and monomeric GADP derivatives.

Intima-media thickness of the carotid artery in hypertensive subjects and hypertrophic cardiomyopathy patients

While hypertension is known to cause left ventricular and vascular hypertrophy, the relationship between alterations of vascular and cardiac structures in patients with hypertrophic cardiomyopathy has not been fully clarified. We measured intima-media thickness of carotid arteries by ultrasonography in patients with hypertrophic cardiomyopathy (n = 16), normotensive subjects (n = 358), and hypertensive subjects (n = 386) in a cohort of 7940 male employees of a bus company. Our object was to determine whether vascular alteration occurs in hypertrophic cardiomyopathy similarly as in hypertension. Hypertrophic cardiomyopathy (wall thickness > or = 15 mm; asymmetrical hypertrophy without hypertension) was screened with family history and electrocardiography followed by echocardiography. The intima-media thickness in patients with hypertrophic cardiomyopathy (mean, 0.61 mm) did not differ from that of normotensive subjects (0.60 mm) but was significantly less than that of hypertensive subjects with left ventricular hypertrophy (wall thickness > or = 14 mm; n = 22; 0.73 mm). In a scatterplot of intima-media thickness versus interventricular septal thickness, these two parameters were significantly correlated in normotensives and hypertensives. The patients with hypertrophic cardiomyopathy distributed outside the 95% confidence range of the normotensive and hypertensive subjects. In summary, the increase in intima-media thickness of the carotid artery paralleled left ventricular hypertrophy in normotensive and hypertensive subjects. Patients with hypertrophic cardiomyopathy had a normal intima-media thickness regardless of the hypertrophied left ventricle. Thus, information on intima-media thickness may be useful in differentiating hypertensive left ventricular hypertrophy from hypertrophic cardiomyopathy.

Bni1p implicated in cytoskeletal control is a putative target of Rho1p small GTP binding protein in Saccharomyces cerevisiae

The RHO1 gene encodes a homolog of mammalian RhoA small GTP binding protein in the yeast Saccharomyces cerevisiae. Rho1p is localized at the growth sites, including the bud tip and the cytokinesis site, and is required for bud formation. We have recently shown that Pkc1p, a yeast homolog of mammalian protein kinase C, and glucan synthase are targets of Rho1p. Using the two-hybrid screening system, we cloned a gene encoding a protein which interacted with the GTP-bound form of Rho1p. This gene was identified as BNI1, known to be implicated in cytokinesis or establishment of cell polarity in S.cerevisiae. Bni1p shares homologous domains (FH1 and FH2 domains) with proteins involved in cytokinesis or establishment of cell polarity, including formin of mouse, capu and dia of Drosophila and FigA of Aspergillus. A temperature-sensitive mutation in which the RHO1 gene was replaced by the mammalian RhoA gene showed a synthetically lethal interaction with the bni1 mutation and the RhoA bni1 mutant accumulated cells with a deficiency in cytokinesis. Furthermore, this synthetic lethality was caused by the incapability of RhoA to activate Pkc1p, but not glucan synthase. These results suggest that Rho1p regulates cytoskeletal reorganization at least through Bni1p and Pkc1p.

Signaling toward yeast 1,3-beta-glucan synthesis

1,3-beta-glucan synthase catalyzes the synthesis of a 1,3-beta-linked glucan polymer which produces the main rigidity of the yeast cell wall. Recent success in purification of this enzyme by product entrapment (21) has provided new insights into the dynamic aspects of the cell wall. This relatively simple procedure made it possible to identify the genes encoding the catalytic subunits of glucan synthase. In addition, the involvement of a rho type GTPase in the regulation of glucan synthase was demonstrated with the purified enzyme. Based on intracellular localization of the glucan synthase subunits, we have proposed a model in which assembly of the subunits is important for the activation of glucan synthase at sites of polarized growth. In this article, we will focus on biochemistry of 1,3-beta-glucan synthase and signaling through rho type GTPase.

Mutational analysis of the beta-subunit of yeast geranylgeranyl transferase I

The gene CAL1 (also known as CDC43) of Saccharomyces cerevisiae encodes the beta subunit of geranylgeranyl transferase I (GGTase I), which modifies several small GTPases. Biochemical analyses of the mutant enzymes encoded by cal1-1, and cdc43-2 to cdc43-7, expressed in bacteria, have shown that all of the mutant enzymes possess reduced activity, and that none shows temperature-sensitive enzymatic activities. Nonetheless, all of the cal1/cdc43 mutants show temperature-sensitive growth phenotypes. Increase in soluble pools of the small GTPases was observed in the yeast mutant cells at the restrictive temperature in vivo, suggesting that the yeast prenylation pathway itself is temperature sensitive. The cal1-1 mutation, located most proximal to the C-terminus of the protein, differs from the other cdc43 mutations in several respects. An increase in soluble Rho1p was observed in the cal1-1 strain grown at the restrictive temperature. The temperature-sensitive phenotype of cal1-1 is most efficiently suppressed by overproduction of Rho1p. Overproduction of the other essential target, Cdc42p, in contrast, is deleterious in cal1-1 cells, but not in other cdc43 mutants or the wild-type strains. The cdc43-5 mutant cells accumulate Cdc42p in soluble pools and cdc43-5 is suppressed by overproduction of Cdc42p. Thus, several phenotypic differences are observed among the cal1/cdc43 mutations, possibly due to alterations in substrate specificity caused by the mutations.

ROM7/BEM4 encodes a novel protein that interacts with the Rho1p small GTP-binding protein in Saccharomyces cerevisiae

The RHO1 gene encodes a homolog of the mammalian RhoA small GTP-binding protein in the yeast Saccharomyces cerevisiae. Rho1p is localized at the growth site and is required for bud formation. The RHO1(G22S, D125N) mutation is a temperature-sensitive and dominant negative mutation of RHO1, and a multicopy suppressor of RHO1(G22S, D125N), ROM7, was isolated. Nucleotide sequencing of ROM7 revealed that it is identical to the BEM4 gene (GenBank accession number L27816), although its physiological function has not yet been reported. Disruption of BEM4 resulted in the cold- and temperature-sensitive growth phenotypes, and cells of the deltabem4 mutant showed abnormal morphology, suggesting that BEM4 is involved in the budding process. The temperature-sensitive growth phenotype was suppressed by overexpression of RHO1, ROM2, which encodes a Rho1p-specific GDP/GTP exchange factor, or PKC1, which encodes a target of Rho1p. Moreover, glucan synthase activity, which is activated by Rho1p, was significantly reduced in the deltabem4 mutant. Two-hybrid and biochemical experiments revealed that Bem4p directly interacts with the nucleotide-free form of Rho1p and, to lesser extents, with the GDP- and GTP-bound forms of Rho1p, although Bem4p showed neither GDP/GTP exchange factor, GDP dissociation inhibitor, nor GTPase-activating protein activity toward Rho1p. These results indicate that Bem4p is a novel protein directly interacting with Rho1p and is involved in the RHO1-mediated signaling pathway.

Impaired action of levcromakalim on ATP-sensitive K+ channels in mesenteric artery cells from spontaneously hypertensive rats

The purpose of the present study was to test the hypothesis that properties of ATP-sensitive K+ channels are altered in arterial smooth muscle cells of hypertensive rats. Using a patch-clamp technique, we compared effects of a K+ channel opener, levromakalim, on membrane currents in mesenteric artery cells from adult Wistar Kyoto rats (WKY) and age-matched spontaneously hypertensive rats (SHR) treated or not treated with hydralazine. Blood pressure was significantly higher in SHR than in WKY or hydralazine-treated SHR. Levcromakalim evoked a time-independent and voltage-insensitive current in a dose-dependent manner in the whole-cell clamp configuration. The reversal potential of the evoked current depended on extracellular K+ concentration. Application of 3 micromol/L glibenclamide, a specific blocker of ATP-sensitive K+ channels, abolished the levcromakalim-evoked current; however, the current was unaffected by either 1 mmol/L tetraethylammonium or 0.3 micromol/L charybdotoxin. These results suggest that the levcromakalim-evoked current was carried through ATP-sensitive K+ channels. In SHR cells, the maximal slope conductance of the levcromakalim-evoked current, normalized by cell capacitance, was decreased, and the dose-response curve was shifted to the right compared with WKY cells. The levcromakalim action was not impaired in cells from hydralazine-treated SHR. In conclusion, the action of levcromakalim on ATP-sensitive K+ channels in SHR mesenteric artery muscle cells was impaired compared with WKY cells. This impairment was corrected by long-term antihypertensive treatment.

Folding-dependent in vitro protein splicing of the Saccharomyces cerevisiae VMA1 protozyme

VMA1 translational product undergoes excision of a 50-kDa intervening segment (VDE: VMA1-derived endonuclease) and religation of the flanking regions to create a 69-kDa catalytic subunit of vacuolar membrane H+-ATPase. VDEs conjugated with polypeptides at both N- and C-terminal ends were expressed in Escherichia coli and examined for their ability to catalyze self-splicing. Processed VDE was found in soluble pools, while unspliced precursors accumulated in insoluble pools, forming inclusion bodies. We demonstrate in vitro protein splicing by refolding of the denatured precursor molecules. The processing reaction efficiently occurs with the purified precursor peptide. VDE bracketed by only 6 proximal and 4 distal amino acids is autocatalytically processed.