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Y S Zhu

Publications and source records attributed to Y S Zhu.

At least 19 recordsLinked to original sources
PubMed1992

Efficient secretion in yeast based on fragments from K1 killer preprotoxin.

The alpha and beta components of the secreted K1 killer toxin of Saccharomyces cerevisiae are derived from residues 45-147 and 234-316, respectively, of the 316 residue preprotoxin (ppTox). The beta N-terminus is produced by Kex2 cleavage after Lys Arg233; when beta la (the mature sequence of beta-lactamase) is fused at this site and the fusion is expressed from the PGK promoter in pDT17, a multicopy plasmid, unexpectedly modest levels of beta la secretion resulted. Over-expression of Kex2 failed to increase beta la secretion while a kex2-null mutation reduced secretion by 98%. beta la secretion in a Kex+ strain was not enhanced by inactivation of the alpha toxin component or by deletion of most of its central hydrophobic segments. However SP-beta la, produced by deletion of ppTox residues 35-176, expressed 10-fold higher beta la activity and the precursor was now secreted with similar efficiency in a kex2-null strain. Fusions of beta la to ppTox at Ala34 or Ala46 also led to efficient secretion in both KEX2 and kex2-null strains. Since these beta la fusions differ only in segments well downstream of the signal peptide and all had similar transcript levels, the efficiency of beta la secretion is apparently determined by the efficiency with which these fusions are translocated to the Golgi compartment where Kex2 is active. Efficiency is high for the shorter fusions, but is 10% or less for the longer fusions; even this fraction is apparently diverted to the vacuole if not cleaved by Kex2. SP-beta la was the most efficient construct tested; secreted beta la reached 4% of total cell protein, modestly exceeding levels produced by fusion to the MF alpha 1-encoded prepro alpha-factor, suggesting potential for the production of foreign proteins in yeast.

Amino Acid Sequence↗
PubMed1992

Time course of enkephalin mRNA and peptides in cultured rat adrenal medulla.

Explantation of rat adrenal medullae to organ culture results in dramatic changes in enkephalins and catecholamines that are similar to the changes seen in vivo in response to denervation, which eliminates transsynaptic impulse activity. We have used rapid and sensitive solution hybridization methods to measure preproenkephalin (PPenk) mRNA and total cellular RNA in samples from rat tissues and adrenal medullary explants. The profiles of adrenal medullary PPenk mRNA, enkephalin-containing (EC) peptides, total cellular RNA and catecholamines [epinephrine (epi) and norepinephrine (norepi)] were measured during 14 days of organ culture. After 8 h in culture, total RNA had declined by 60%, epi and norepi declined 80 to 85% and EC peptides by 50% while the amount of PPenk mRNA per gland increased by 400%. Between 8 h and 14 days total RNA and catecholamine levels remained constant while PPenk mRNA increased to a peak of 85 +/- 10 (S.E.M.) pg/gland at 2-4 days, a value that was 80 times greater than the zero time (preculture) values. EC peptide levels lagged behind the increase in PPenk mRNA and reached a peak of 25 +/- 4 (S.E.M.) pmol Met-enkephalin equivalents/gland at 4 days that was 80 times greater than zero time values. Both PPenk mRNA and EC peptides declined in parallel between 4 and 14 days. The ratio of the copies of proenkephalin (Penk) peptide to PPenk mRNA was estimated to be 25,000 at the time of explantation and after 4 days in culture. From steady-state kinetics half-life estimates of 9.6 h for PPenk mRNA and 14.7 h for Penk peptide were obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Medulla↗
PubMed1992

Kex2-dependent processing of yeast K1 killer preprotoxin includes cleavage at ProArg-44.

The K1 killer toxin of Saccharomyces cerevisiae consists of 103- and 83-residue alpha and beta components whose derivation, from a 316-residue precursor preprotoxin, requires processing at the alpha N-terminus (after ProArg-44), the alpha C-terminus (after ArgArg-149) and at the beta N-terminus (after LysArg-233). These processing events occur after translocation to the Golgi and have been investigated using beta-lactamase fusions. Signal peptidase cleavage of the precursor, predicted to occur after Ala-26, was confirmed by N-terminal sequence analysis of Ala-34 and Ile-52 fusions. Cleavage at all of the other predicted processing sites, including ProArg-44, is dependent on activity of the Kex2 protease. A fourth Kex2-dependent cleavage occurs at LysArg-188. Implications for the specificity of Kex2 cleavage and preprotoxin processing are discussed.

Amino Acid Sequence↗
PubMed1991

Preproenkephalin mRNA and enkephalin in normal and denervated adrenals in the Syrian hamster: comparison with central nervous system tissues.

The distribution and characteristics of preproenkephalin (PPenk) mRNA and enkephalin-containing (EC) peptides are compared in CNS and adrenal tissues from Syrian hamsters and Sprague-Dawley rats. Total cellular RNA extracts from both rat and hamster tissues produce a single hybridization band of PPenk mRNA of approximately 1500 bases when analyzed by Northern blot hybridization. Quantitation by solution hybridization reveals that in the hamster the highest levels of PPenk mRNA are found in adrenal (16.3 +/- 1.4 pg equivalents/micrograms RNA (mean +/- S.E.M.)) and striatum (13.3 +/- 0.7), followed by hypothalamus (0.8 +/- 0.2), and hippocampus (0.4 +/- 0.2). In the rat the highest levels of PPenk mRNA are in the striatum (35 +/- 2 pg/micrograms RNA) followed by the hypothalamus (3.0 +/- 0.5), hippocampus (0.3 +/- 0.1) and adrenal (0.18 +/- 0.04). Thus, the rank order of abundance of PPenk mRNA is similar in these CNS tissues for rat and hamster. The hamster adrenal levels are more than 90-fold greater than those of the rat. The abundance of EC peptides in both hamster and rat tissues mirror the rank order found with PPenk mRNA. Hamster adrenal contains the highest level of EC peptides (441 +/- 37 pmol/mg protein (mean +/- S.E.M.)) which is more than 400-fold greater than that of the rat adrenal and 8- to 12-fold greater than that found in rat and hamster striatum or hypothalamus. Both size exclusion chromatography and Western blot analysis indicate that EC peptides in hamster adrenal are predominantly large proenkephalin-like peptides with approximately 6 copies of Met- and 1 copy of Leu-enkephalin and that included in their number is a prominent EC peptide with a molecular weight of 34 kDa. Unilateral denervation of the hamster adrenal results in a time-dependent ipsilateral decrease in EC peptide and PPenk mRNA levels. Thus, by day 8 postsurgery, PPenk mRNA levels have declined by an average of 80% while EC peptides are reduced by 68% when compared to the innervated contralateral adrenal. These results demonstrate the great abundance of PPenk mRNA and EC peptides in the hamster adrenal. They also demonstrate the apparent need for transsynaptic impulse activity to maintain the high steady-state levels of PPenk and EC peptides. These characteristics of the hamster adrenal system provide opportunities for physiological and pharmacological investigations of the regulation of proenkephalin gene expression.

Adrenal Glands↗
PubMed1991

Applications of adaptive filtering to ECG analysis: noise cancellation and arrhythmia detection.

Several adaptive filter structures are proposed for noise cancellation and arrhythmia detection. The adaptive filter essentially minimizes the mean-squared error between a primary input, which is the noisy ECG, and a reference input, which is either noise that is correlated in some way with the noise in the primary input or a signal that is correlated only with ECG in the primary input. Different filter structures are presented to eliminate the diverse forms of noise: baseline wander, 60 Hz power line interference, muscle noise, and motion artifact. An adaptive recurrent filter structure is proposed for acquiring the impulse response of the normal QRS complex. The primary input of the filter is the ECG signal to be analyzed, while the reference input is an impulse train coincident with the QRS complexes. This method is applied to several arrhythmia detection problems: detection of P-waves, premature ventricular complexes, and recognition of conduction block, atrial fibrillation, and paced rhythm.

Algorithms↗
PubMed1991

Transsynaptic activity regulates proenkephalin and tyrosine hydroxylase gene expression and the response to reserpine in the hamster adrenal.

Transsynaptic neurogenic activity and reserpine are two signals that cause the proenkephalin (Penk) gene to alter the levels of preproenkephalin (PPenk) mRNA and enkephalin-containing (EC) peptides. In the Syrian hamster adrenal, but not in rat adrenal, both of these signals appear to be positive activators of Penk gene expression. The separate and combined effects of reserpine and denervation on EC peptides and catecholamine systems were investigated in the adrenal of the hamster, a species with relatively high medullary PPenk mRNA and EC peptide levels. Unilateral adrenal denervation resulted in a rapid decrease in PPenk mRNA levels of 54% after 2 days, and by 11 days 90% of Penk mRNA had disappeared. After 4 days both EC peptide and PPenk mRNA levels fell in parallel, whereas total RNA and soluble protein levels were unchanged. Denervation had no effect on TH mRNA levels until 8 days after surgery, and after 11 days both TH mRNA and catecholamine levels had decreased by 35-45%. Reserpine produced a dose- and time-dependent depletion of EC peptides and catecholamines. One day after 5 mg/kg reserpine (given subcutaneously on each of 2 consecutive days), EC peptides were reduced by 80%, norepinephrine by 79%, and epinphrine by greater than 95%. By 4 days after treatment, EC peptides and catecholamines slightly exceeded or had returned to control (concurrent vehicle treatment) values. PPenk mRNA levels, as measured by solution hybridization, were doubled (206 +/- 17%, mean +/- standard error) by day 4. Tyrosine hydroxylase (TH) mRNA levels were increased nearly 7-fold (686 +/- 71%) 24 hr after the first reserpine dose and declined thereafter. Northern blot analysis demonstrated that reserpine did not alter the size of either PPenk or TH mRNAs. Size exclusion chromatography showed a small (20%) reserpine-induced increase in processing of high molecular weight Penk-like peptides. The effects of reserpine, which increases PPenk mRNA, EC peptides, and TH mRNA, were completely blocked by unilateral denervation, whereas the contralateral innervated gland showed the expected responses. The co-localized EC peptide and catecholamine systems, as reflected in their mRNAs, respond differently in both time sequence and magnitude to reserpine and to denervation. Our results support a critical role, in vivo, for transsynaptic mechanisms in the maintenance of the high levels of Penk gene expression in this species and for the positive activation (mediated by reflex neurogenic stimulation) of reserpine on Penk and TH gene expression.

Adrenal Glands↗
PubMed1990

Ventricular tachycardia and fibrillation detection by a sequential hypothesis testing algorithm.

An algorithm for detecting ventricular fibrillation (VF) and ventricular tachycardia (VT) by the method of sequential hypothesis testing is presented. The algorithm first generates a binary sequence by comparing the signal to a threshold. The probability distribution of the time intervals of the binary sequence is obtained, and Wald's sequential hypothesis testing procedure is next employed to discriminate the arrhythmias. Sequential hypothesis testing of 85 cases resulted in identification of 1) 97.64% VF and 97.65% VT episodes after 5 s, and 2) 100% identification of both VF and VT after 7 s. The desired false positive and false negative error probabilities can be preprogrammed into the algorithm. An important feature of the sequential method is that extra time for detection can be traded off for improved accuracy, and vice versa.

Algorithms↗
PubMed1990

Central opioid modulation of fetal cardiovascular function: role of mu- and delta-receptors.

To investigate the role of mu- and delta-receptors in opioid modulation of fetal cardiovascular function, we compared the effects on fetal heart rate (FHR) and fetal blood pressure (FBP) of [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAGO, a mu-selective agonist), [D-Pen2,D-Pen5]-enkephalin (DPDPE, delta-selective agonist), and [D-Ala2,D-Leu5]-enkephalin (DADLE, a mixed mu- and delta-agonist) in 24 fetal lambs. All peptides were infused intracerebroventricularly at a constant rate for 1 h. Three to seven animals were studied at each of six dose levels ranging from 1.58 to 476 nmol/h. Saline infusion did not elicit any changes in FBP or FHR. DAGO caused a dose-dependent increase in FHR, with the peak response being 61.6 +/- 9.9% at the highest dose. The effects of DAGO on FBP were small (maximum being 11.1 +/- 3.4%) and did not reach statistical significance. In contrast, DPDPE did not induce any changes in either FHR or FBP over the same dose range, suggesting that delta-receptors do not play a role in opioid modulation of fetal cardiovascular function. The FHR response to DADLE was similar to DAGO in both dose-response and time-action characteristics. The finding that DADLE behaved like DAGO rather than DPDPE suggests that the opioid-induced fetal tachycardia may be mediated via mu 1-receptors. There was also evidence for rapid development of tolerance to the FHR response to both DAGO and DADLE, as demonstrated by the decline in FHR response by 45-50 min despite continuous peptide infusion.

Analysis of Variance↗
PubMed1989

Morphine-induced tachycardia in fetal lambs: a bell-shaped dose-response curve.

A dose-response analysis of the effects of morphine on fetal heart rate (FHR) and blood pressure (FBP) was conducted in 28 chronically instrumented fetal lambs. Morphine was infused directly to the fetus at doses ranging from 0.075 to 40 mg/hr. At doses below 0.15 mg/hr, morphine did not result in significant changes in FHR or FBP. With increasing doses of morphine, fetal tachycardia was observed without significant changes in FBP, and the peak response (38.3 +/- 8%) in FHR was reached at a dose of 2.5 mg/hr. Further increases in dose were associated with a decrease in the magnitude of response. This resulted in a bell-shaped dose-response curve. This tachycardia was completely abolished by either naloxone or propranolol pretreatment. These results indicate that i.v. morphine administrated produces tachycardia in unanesthetized unrestrained fetal lambs, and this effect is mediated via specific opioid receptors and involves the beta adrenergic system.

Animals↗
PubMed1988

Transcription of oxygen-regulated photosynthetic genes requires DNA gyrase in Rhodobacter capsulatus.

The regulation of the photosynthetic genes by DNA supercoiling in Rhodobacter capsulatus has been studied by using gyrase inhibitors in vivo and by measurement of mRNA levels of more than a dozen genes. The results demonstrate that the levels of mRNA for light-harvesting (I, II) and reaction center (L, M, H) proteins, bacteriochlorophyll biosynthetic enzymes, ribulose-bisphosphate carboxylase (EC 4.1.1.39), and the mRNAs from the open reading frames Q and R decreased immediately and dramatically upon addition of novobiocin and coumermycin. In contrast, the mRNAs for carotenoid biosynthetic enzymes, the cytochrome bc1 complex, and constitutively expressed mRNA under aerobic conditions for light-harvesting I and for reaction center (L, M) proteins are less sensitive to the inhibitors. In accordance with these results, the biosynthesis of bacteriochlorophyll is markedly repressed by gyrase inhibitors novobiocin, coumermycin, nalidixic acid, and oxolinic acid either under anaerobic conditions or during a shift from aerobic to anaerobic conditions. The synthesis of light-harvesting (I, II) bacteriochlorophyll complexes is also inhibited by novobiocin and coumermycin. The kinetics of specific mRNA changes and the differential sensitivity of anaerobic and aerobic genes to the gyrase inhibitors strongly suggest that DNA supercoiling is involved in the differential expression of photosynthetic genes in response to the level of oxygen in R. capsulatus.

Aerobiosis↗
PubMed1988

Prenatal morphine exposure and sleep-wake disturbances in the fetus.

We have previously shown that acute exposure to low-dose morphine stimulates arousal and breathing movements in the fetal lamb. We now report on the effects of subacute low-dose morphine exposure on the regulation of fetal sleep-wake behavior and breathing patterns. Morphine was infused to 11 fetal lambs (121-129 days gestation) at a constant rate of 400 micrograms/h for 7 days via a mini osmotic pump implanted subcutaneously in the maternal flank and connected directly to an indwelling catheter in the fetal vena cava. On day 1, morphine resulted in a state of arousal in all fetuses, with loss of quiet sleep and rapid eye movement (REM) sleep. This response was greatly reduced by day 2 and was insignificant by day 3, despite continuous drug exposure. There was no decrease in plasma morphine levels. Two fetuses died during morphine exposure. Upon removal of the pump, all fetuses exhibited disturbances in their sleep cycles within 1-3 h, with an increase in arousal time and loss of REM sleep. The duration of the arousal and quiet sleep episodes was also greatly reduced. Such disturbances were noted for 3-4 days after termination of morphine infusion. Four fetuses were delivered prematurely (131-136 days) during this period. These results demonstrate the rapid onset of tolerance to low-dose morphine exposure in the fetus and the development of physical dependence, as manifested by a mild abstinence syndrome characterized by sleep-wake disturbances.

Animals↗
PubMed1988

Dual action of morphine on fetal breathing movements.

Morphine has been reported to both stimulate and suppress fetal breathing movements (FBM). In light of these conflicting reports, we have conducted a systematic dose-response analysis of the effects of morphine on FBM in 27 fetal lambs. Morphine was infused directly to the fetus in doses ranging from 0.075 to 80 mg/hr. Low doses (0.075-2.5 mg/hr) resulted in a progressive increase in the relative incidence of FBM, whereas higher doses (greater than 2.5 mg/hr) decreased FBM with total apnea observed at 80 mg/hr. This biphasic response can be fitted as the sum of two sigmoidal log dose-response curves. Both stimulation and suppression of FBM by morphine were abolished by naloxone pretreatment, indicating that both responses are mediated by activation of opioid receptors. The dual action of morphine on FBM may be due to different opioid receptor subtypes or different sites of action.

Animals↗
PubMed1987

Cyclic variation in fetal heart rate and sympathetic activity.

The effects of alpha- and beta-adrenergic blockade on electrocortical activity-related cyclic variability in fetal heart rate and mean arterial pressure were investigated in eight fetal lambs between 119 and 138 days of gestation. In the absence of adrenergic blockade, fetal heart rate during high-voltage slow activity was significantly higher than that during low-voltage fast activity. Propranolol (2.0 mg/hr) produced a decrease in fetal heart rate, but the decrease was only statistically significant during high-voltage slow activity. Phentolamine (5.0 mg/hr) induced a significant increase in fetal heart rate with a small but statistically significant decrease in mean arterial pressure. The cyclic variability in fetal heart rate between low-voltage fast activity and high-voltage slow activity was abolished by propranolol and enhanced by phentolamine. These results indicate that the cyclic variability in the fetal heart rate associated with electrocortical activity can be accounted for by cyclic fluctuation in sympathetic activity.

Animals↗
PubMed1986

Origin of the mRNA stoichiometry of the puf operon in Rhodobacter sphaeroides.

The LH-I structural genes are located 5' of the RC-L and -M structural genes on what has been designated as the puf operon of Rhodobacter sphaeroides. Analysis of puf operon expression in R. sphaeroides by Northern hybridization with probes specific for individual structural gene has identified two transcripts encoded by this operon. The large (2.6 kilobase pairs (kb] transcript contains sequences for all four polypeptides of the puf operon, whereas the small (0.5 kb) transcript, which is more abundant (10-15-fold) than the large transcript under photosynthetic growth, is homologous only to the two LH-I structural genes. Transcription of the puf operon during photosynthetic growth under saturating light conditions is increased approximately 3-fold relative to growth in the presence of oxygen while the relative ratio of these two transcripts is independent of the incident light intensity. Analysis of the turnover of the two transcripts (t1/2 of 9 and 20 min for the large and small transcripts, respectively) indicates that 5' processing is the initial step in the degradation of the large transcript and that the molar excess of the small transcript cannot be accounted for by differences in the rates of turnover of these two mRNA species. Analysis of the 5' ends of the 2.6- and 0.5-kb transcripts, their relative abundance, and stabilities indicates that these two transcripts have different 5'-ends corresponding to 75 and 104 base pairs upstream from the start of the LH-I beta structural gene, respectively. Northern hybridization analysis with specific synthetic deoxyoligonucleotide probes confirmed that the two transcripts differ by 29 bases at their 5'-ends, suggesting that differential transcript initiation may be involved in regulating the relative levels of these two mRNA species in vivo, although we cannot rule out complex mechanisms of post-transcriptional processing.

Bacterial Proteins↗
PubMed1986

Regulation of expression of genes for light-harvesting antenna proteins LH-I and LH-II; reaction center polypeptides RC-L, RC-M, and RC-H; and enzymes of bacteriochlorophyll and carotenoid biosynthesis in Rhodobacter capsulatus by light and oxygen.

RNA levels were measured by blot hybridization to study the coordinate and differential expression of Rhodobacter capsulatus genes for light-harvesting I antenna proteins LH-I and LH-II; reaction center (RC) polypeptides L, M, and H; and bacteriochlorophyll and carotenoid biosynthesis in response to light and O2. The genes for LH-II alpha and beta subunits only have one transcript, 0.5 kilobase (kb) long, whereas the genes for LH-I have two transcripts (0.5 and 2.6 kb). The small transcript (0.5 kb) is the mRNA only for LH-I beta and alpha polypeptides, whereas the large transcript (2.6 kb) codes for RC-L, RC-M, and the beta and alpha polypeptides of LH-I, as well as the product of an unknown open reading frame designated ORF C2397. These five genes thus comprise a single operon (designated the puf operon). The mRNA specifying the LH-II polypeptides is more abundant, more sensitive to changes in O2 concentration, and shows a variation over a wider range than that of the mRNA for LH-I, indicating that the genes for LH-II and LH-I/RC are regulated independently. The gene for RC-H (puhA) has at least two transcripts (1.2 and 1.4 kb) that initiate within ORF F1696 and respond differentially to light intensity. The expression of the genes coding for RC-L, RC-M, and RC-H is coordinately regulated by light intensity and O2 concentration. An increase in light intensity causes a decrease in the expression of the genes for LH-I, LH-II, and RC proteins. The genes coding for the enzymes in the bacteriochlorophyll biosynthetic pathways are regulated by light intensity and O2 in a manner similar to that of the genes for LH and RC proteins. The crt genes coding for the enzymes in carotenoid biosynthetic pathways, however, are regulated in an opposite fashion: high light intensity results in increased expression of crt genes. These results are interpreted based on the protective function of carotenoids under high light intensity in the presence of O2.

Bacterial Proteins↗