Dependence of the regulation of telomere length on the type of subtelomeric repeat in the yeast Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae, chromosomes terminate with approximately 400 bp of a simple repeat poly(TG(1-3)). Based on the arrangement of subtelomeric X and Y' repeats, two types of yeast telomeres exist, those with both X and Y' (Y' telomeres) and those with only X (X telomeres). Mutations that result in abnormally short or abnormally long poly(TG(1-3)) tracts have been previously identified. In this study, we investigated telomere length in strains with two classes of mutations, one that resulted in short poly(TG(1-3)) tracts (tel1) and one that resulted in elongated tracts (pif1, rap1-17, rif1, or rif2). In the tel1 pif1 strain, Y' telomeres had about the same length as those in tel1 strains and X telomeres had lengths intermediate between those in tel1 and pif1 strains. Strains with either the tel1 rap1-17 or tel1 rif2 genotypes had short tracts for all chromosome ends examined, demonstrating that the telomere elongation characteristic of rap1-17 and rif2 strains is Tel1p-dependent. In strains of the tel1 rif1 or tel1 rif1 rif2 genotypes, telomeres with Y' repeats had short terminal tracts, whereas most of the X telomeres had long terminal tracts. These results demonstrate that the regulation of telomere length is different for X and Y' telomeres.     

The effect of base sequence on the stability of RNA and DNA single base bulges

Forty-eight RNA duplexes were constructed that contained all common single base bulges at six different locations. The stabilities of the RNAs were determined by temperature gradient gel electrophoresis (TGGE). The relative stability of a single base bulge was dependent on both base identity and the nearest neighbor context. The single base bulges were placed into two categories. A bulged base with no identical neighboring base was defined as a Group I base bulge. Group II-bulged bases had at least one neighboring base identical to it. Group II bulges were generally more stable than Group I bulges in the same nearest neighbor environments. This indicates that position degeneracy of an unpaired base enhances stability. Differences in the mobility transition temperatures between the RNA fragments with bulges and the completely base-paired reference RNAs were related to free energy differences. Simple models for estimating the free energy contribution of single base bulges were evaluated from the free energy difference data. The contribution of a Group I bulge 5'-(XNZ)-3'.5'-(Z'-X')-3' where N is the unpaired base and X.X' and Z.Z' the neighboring base pairs, could be well-represented (+/-0.34 kcal/mol) by the equation, DeltaG((X)(N)()(Z))(.)((Z)(')(-)(X)(')()) = 3.11 + 0. 40DeltaG(s)()((XZ))(.)((Z)(')(X)(')()). DeltaG(s)()((XZ))(. )((Z)(')(X)(')()) is the stacking energy of the closing base pair doublet. By adding a constant term, delta = -0.3 kcal/mol, to the right side of the above equation, free energies of Group II bulges could also be predicted with the same accuracy. The term delta represents the stabilizing effect due to position degeneracy. A similar equation/model was applied to previous data from 32 DNA fragments with single base bulges. It predicted the free energy differences with a similar standard deviation.     

Distribution of telomere-associated sequences on natural chromosomes in Saccharomyces cerevisiae.

Pulsed-field gel electrophoresis was used to examine the distribution of telomere-associated sequences on individual chromosomes in four strains of Saccharomyces cerevisiae. The pattern of X and Y' distribution was different for each strain. At least one chromosome in each strain lacked Y', and in some strains, chromosome I, the smallest yeast chromosome, lacked detectable amounts of both X and Y'.     

Properties of proteins produced after damage to deoxyribonucleic acid of Escherichia coli.

Large amounts of extra proteins, X (in the envelope fraction) and X' (in the cytoplasmic fraction) were detected by SDS-polyacrylamide gel electrophoresis when DNA of Escherichia coli was damaged. These two proteins had the same apparent molecular weight (appproximately 40,000) and were produced under identical conditions, including requirement for the recA" and lexA+ genotype. Sucrose density gradient centrifugation revealed that protein X' consisted of relatively large and heterogeneous aggregates in the cytoplasmic fraction; the distribution of protein X in the envelope was not determined. As proteins X and X' were shown to be equivalent, it is suggested that they are identical. Co-precipitation of the aggregates of protein X' with the envelope led to the appearance of protein X in the envelope fraction.     

Binding specificities of actinomycin D to non-self-complementary -XGCY-tetranucleotide sequences.

Studies on the binding specificity of actinomycin D (ACTD) to tetranucleotide sequences of the form -XGCY- have been extended to include the non-self-complementary sequences. ACTD binding characteristics are investigated by equilibrium, kinetic, and thermal denaturation for decameric duplexes d(ATA-XGCY-ATA)-d(TAT-Y'GCX'-TAT), where X and Y are complementary to X' and Y', respectively, but not to each other. The results indicate that when X = G or Y = C, the oligomers exhibit significantly weaker ACTD binding affinities, smaller melting temperature increases upon drug binding, and faster SDS-induced ACTD dissociation rates than the other sequences. Estimated binding constants at 18.5 degrees C for decameric duplexes containing -AGCA-/-TGCT-, -AGCG-/-CGCT-, or -CGCA-/-TGCG- are in the range of 4-9 microM-1, whereas for the ones containing -GGCT-/-AGCC-, -GGCA-/-TGCC-, or -GGCG-/-CGCC- they range from 0.6 to 2 microM-1. In contrast to the characteristic SDS-induced ACTD dissociation times of 600-1000 s for the stronger binding sites, the sequences containing X = G or Y = C exhibit at least an order of magnitude faster dissociation kinetics. These observations are further supported by the induced CD results and fluorescence measurements with 7-amino-ACTD. The findings from these non-self-complementary -XGCY- tetranucleotide sequences are consistent with those found earlier for the self-complementary counterparts, and they together clearly demonstrate that a base sequence alteration adjacent to the GC site can have a profound effect on the ACTD binding as well as dissociation characteristics, likely a consequence of subtle conformational alterations near the binding site.(ABSTRACT TRUNCATED AT 250 WORDS)     

小云斑鳃金龟雌蛹羽化动态数学模拟

雌蛹每日羽化数经常用对数代换后计算累积羽化率并转为机率值（Y）羽化日期用儒略历期编码（X）。两者相关回归结果为：Y=14．3490＋0．104lX;r=0．9951。由此回归方程计算每日理论羽化数对数值,并对实际羽化数对数值做适合性检验,得X2=3．69,表明两者之间的适合概率高达99％。文内还以此回归方程确定了雌蛹羽化动态的5个特征日期及其95％置信区间。     

Effects of free radicals on the electrophysiological function of cardiac membranes.

Abnormal electrical activity in heart cells can result in irregular heart rhythms or arrhythmias. Any form of pathological or toxicological damage to the sarcolemmal membrane presents the risk of precipitating arrhythmias and compromise of the heart's function as a pump. An array of cardiovascular conditions from coronary artery disease and myocardial infarction to cardiomyopathies and hypertrophy, can induce arrhythmias. Many of these conditions recently have been linked to increases in free radical production. Early studies suggesting a role for free radicals in the abnormal function of ischemic and reperfused hearts use anti-free radical interventions to reduce arrhythmias. More recent works have taken advantage of different free radical-generating systems to show a reproducible sequence of changes in the cellular action potential; these data suggest changes in the transmembrane movement of ions through membrane channels. Biochemical evidence supports a possible involvement of ion exchange mechanisms in the cardiac sarcolemma. All the evidence indicate that free radical injury may have profound effects on the electrical function of myocardial cells.     

Cohabitation of insulators and silencing elements in yeast subtelomeric regions

In budding yeast, the telomeric DNA is flanked by a combination of two subtelomeric repetitive sequences, the X and Y' elements. We have investigated the influence of these sequences on telomeric silencing. The telomere-proximal portion of either X or Y' dampened silencing when located between the telomere and the reporter gene. These elements were named STARs, for subtelomeric anti-silencing regions. STARs can also counteract silencer-driven repression at the mating-type HML locus. When two STARs bracket a reporter gene, its expression is no longer influenced by surrounding silencing elements, although these are still active on a second reporter gene. In addition, an intervening STAR uncouples the silencing of neighboring genes. STARs thus display the hallmarks of insulators. Protection from silencing is recapitulated by multimerized oligonucleotides representing Tbf1p- and Reb1p-binding sites, as found in STARs. In contrast, sequences located more centromere proximal in X and Y' elements reinforce silencing. They can promote silencing downstream of an insulated expressed domain. Overall, our results suggest that the silencing emanating from telomeres can be propagated in a discontinuous manner via a series of subtelomeric relay elements.     

Identification of autonomously replicating circular subtelomeric Y'' elements in Saccharomyces cerevisiae.

We marked a large number of yeast telomeres within their Y' regions by transforming strains with a fragment of Y' DNA into which the URA3 gene had been inserted. A few of the Ura+ transformants obtained were very unstable and were found to contain autonomously replicating URA3-marked circular Y' elements in high copy number. These marked extrachromosomal circles were capable of reintegrating into the chromosome at other telomeric locations. In contrast, most of the Ura+ transformants obtained were quite stable mitotically and were marked at bona fide chromosomal ends. These stable transformants gave rise to mitotically unstable URA3-marked circular Y' elements at a low frequency (up to 2.5%). The likelihood that such excisions and integrations represent a natural process in Saccharomyces cerevisiae is supported by our identification of putative Y' circles in untransformed strains. The transfer of Y' information among telomeres via a circular intermediate may be important for homogenizing the sequences at the ends of yeast chromosomes and for generating the frequent telomeric rearrangements that have been observed in S. cerevisiae.     

Realization of biophysical models of cardiac electrical activity

Considered are the principles of realization of biophysical models of heart ventricle electrical activity in the form of a double electric layer on the surface of the electrically active myocardium (epicardium and endocardium) and the boundary surfaces dividing the model compartments with different electrophysiological characteristics. The model parameters are the electrophysiological and anatomical characteristics of the heart such as the geometry of the ventricles and the specialized His-Purkinje conduction system, the velocity of depolarization spread over myocardium, the ratio of the velocities of excitation transmission through the Myocardium / His / Purkinje elements of the model, the shape of transmembrane action potentials on the boundary surfaces, the orientation of the intrinsic anatomical axes of the heart relative to the initial set of coordinates, and some other biophysical characteristics of the myocardium. This model is the main unit of a computer simulation system, which includes databases of real and simulated electrocardiosignals.     

Energy expenditure during bench press and squat exercises

Despite the popularity of resistance training (RT), an accurate method for quantifying its metabolic cost has yet to be developed. We applied indirect calorimetry during bench press (BP) and parallel squat (PS) exercises for 5 consecutive minutes at several steady state intensities for 23 (BP) and 20 (PS) previously trained men. Tests were conducted in random order of intensity and separated by 5 minutes. Resultant steady state VO2 data, along with the independent variables load and distance lifted, were used in multiple regression to predict the energy cost of RT at higher loads. The prediction equation for BP was Y' = 0.132 + (0.031)(X1) + (0.01)(X2), R2 = 0.728 and S(xy) = 0.16; PS can be predicted by Y' = -1.424 + (0.022)(X1) + (0.035)(X2), R2 = 0.656 and S(xy) = 0.314; where Y' is VO2 X1 is the load measured in kg and X2 is the distance in cm. Based on a respiratory exchange ratio (RER) of 1.0 and a caloric equivalent of 5.05 kcal x L(-1), VO2 was converted to caloric expenditure (kcal x min(-1)). Using those equations to predict caloric cost, our resultant values were significantly larger than caloric costs of RT reported in previous investigations. Despite a potential limitation of our equations to maintain accuracy during very high-intensity RT, we propose that they currently represent the most accurate method for predicting the caloric cost of bench press and parallel squat.     

Titration of aspartate-85 in bacteriorhodopsin: what it says about chromophore isomerization and proton release.

Titration of Asp-85, the proton acceptor and part of the counterion in bacteriorhodopsin, over a wide pH range (2-11) leads us to the following conclusions: 1) Asp-85 has a complex titration curve with two values of pKa; in addition to a main transition with pKa = 2.6 it shows a second inflection point at high pH (pKa = 9.7 in 150-mM KCl). This complex titration behavior of Asp-85 is explained by interaction of Asp-85 with an ionizable residue X'. As follows from the fit of the titration curve of Asp-85, deprotonation of X' increases the proton affinity of Asp-85 by shifting its pKa from 2.6 to 7.5. Conversely, protonation of Asp-85 decreases the pKa of X' by 4.9 units, from 9.7 to 4.8. The interaction between Asp-85 and X' has important implications for the mechanism of proton transfer. In the photocycle after the formation of M intermediate (and protonation of Asp-85) the group X' should release a proton. This deprotonated state of X' would stabilize the protonated state of Asp-85.2) Thermal isomerization of the chromophore (dark adaptation) occurs on transient protonation of Asp-85 and formation of the blue membrane. The latter conclusion is based on the observation that the rate constant of dark adaptation is directly proportional to the fraction of blue membrane (in which Asp-85 is protonated) between pH 2 and 11. The rate constant of isomerization is at least 10(4) times faster in the blue membrane than in the purple membrane. The protonated state of Asp-85 probably is important for the catalysis not only of all-trans <=> 13-cis thermal isomerization during dark adaptation but also of the reisomerization of the chromophore from 13-cis to all-trans configuration during N-->O-->bR transition in the photocycle. This would explain why Asp-85 stays protonated in the N and O intermediates.     

Noninvasive electrocardiographic imaging for cardiac electrophysiology and arrhythmia

Over 7 million people worldwide die annually from erratic heart rhythms (cardiac arrhythmias), and many more are disabled. Yet there is no imaging modality to identify patients at risk, provide accurate diagnosis and guide therapy. Standard diagnostic techniques such as the electrocardiogram (ECG) provide only low-resolution projections of cardiac electrical activity on the body surface. Here we demonstrate the successful application in humans of a new imaging modality called electrocardiographic imaging (ECGI), which noninvasively images cardiac electrical activity in the heart. In ECGI, a multielectrode vest records 224 body-surface electrocardiograms; electrical potentials, electrograms and isochrones are then reconstructed on the heart's surface using geometrical information from computed tomography (CT) and a mathematical algorithm. We provide examples of ECGI application during atrial and ventricular activation and ventricular repolarization in (i) normal heart (ii) heart with a conduction disorder (right bundle branch block) (iii) focal activation initiated by right or left ventricular pacing, and (iv) atrial flutter.     

FIRST HEART SOUND ALTERNANS IN MASSIVE PERICARDIAL EFFUSION

First heart sound alternans in the absence of pulsus alternans, or variation in heart rate (i.e., variation in PR interval), occurring in a patient with massive neoplastic pericardial effusion is described. The mechanism appears to be similar to that in electrical alternans and is shown by echocardiography to be related to the cardiac position within the pericardium, with the first heart sound intensity varying according to the distance of the heart from the chest wall. First heart sound alternans, electrical alternans, and alternating cardiac motion within the pericardium disappeared following pericardiocentesis.     

The use of metallic implants in the study of facial growth in children: method and application

On the basis of experience gained over a number of years, an account is given of the technique for insertion of the implants, the radiographic method, and the graphic procedure for preparation of growth tracings. Small pins of hard tantalum are hammered into the bone under local analgesia with a pencil-shaped instrument, in the tip of which the implant is placed. No surgical exposure is necessary. Because of remodeling resorption of the bone and eruption of the teeth, the implants can be placed only in certain places in the maxilla and mandible. In implant studies it is necessary to observe a high level of reproducibility in positioning the head in the cephalostat. An X -ray cephalostat with a built-in image intensifier has been designed which enables the position to be monitored by televison. In the graphic procedure, drawings of the arches from dental casts are incorporated in tracings of profile radiographs; the paths of eruption of the teeth and development or the arches can then be examined with the metallic implants as references.     

Effects of plasma norepinephrine elevation on the heart's adaptation to chronic aortic constriction in rats

Chronically elevated plasma norepinephrine has the potential for supporting function of diseased hearts, yet may also initiate harmful biochemical and (or) structural changes in the myocardium. The present study investigated the dosage-related effects of chronic norepinephrine infusion on markers of myocardial damage and then tested the influence of a relatively low norepinephrine infusion rate (0.05 microgram X kg-1 X min-1) on the heart's adaptation to pressure overload in aortic constricted rats. Norepinephrine infusion at 0.50 microgram X kg-1 X min-1 led to significantly increased myocardial hydroxyproline concentration and significant mortality. A rate of 0.25 microgram X kg-1 X min-1 increased myocardial hydroxyproline concentration and mortality in aortic constricted rats but had no such effects on sham-operated rats. The lowest rate tested (0.05 microgram X kg-1 X min-1) significantly increased mean arterial pressure and lung weight of aortic constricted rats, without affecting the degree of left ventricular hypertrophy. This infusion rate and aortic constriction each increased plasma norepinephrine and impaired cardiac performance during rapid preloading, although their combination did not cause further impairment. Thus, it appears that even modest plasma norepinephrine elevation has a negative effect on the heart's adaptation to sustained pressure overload.     

I point my heart with the tip of my fingers–Biometry for the diagnosis of congenital heart defects

Congenital heart defects are characterized by abnormal positioning of some anatomical structures relative to a normal heart. Classically the classification of the disease or the stage of the disease is based on the measurement of the relative position of these structures by the cardiac morphologist. We propose a method in which the heart volume is acquired by a CT scanner. In this paper we present a tool which allows us to define landmarks interactively in this heart volume. These landmarks are then used to estimate some simple geometrical models of the anatomical structures and so as to describe their relative position and orientation.