DNA replication forks pause at silent origins near the HML locus in budding yeast

Chromosomal replicators in budding yeast contain an autonomously replicating sequence (ARS) that functions in a plasmid, but certain ARSs are silent as replication origins in their natural chromosomal context. In chromosome III, the HML ARS cluster (ARS302-ARS303-ARS320) and ARS301 flank the transcriptionally silent mating-type locus HML, and all of these ARSs are silent as replication origins. ARS301 and ARS302 function in transcriptional silencing mediated by the origin recognition complex (ORC) and a heterochromatin structure, while the functions of ARS303 and ARS320 are not known. In this work, we discovered replication fork pause sites at the HML ARS cluster and ARS301 by analyzing DNA replication intermediates from the chromosome via two-dimensional gel electrophoresis. The replication fork pause at the HML ARS cluster was independent of cis- and trans-acting mutations that abrogate transcriptional silencing at HML. Deletion of the HML ARS cluster led to loss of the pause site. Insertion of a single, heterologous ARS (ARS305) in place of the HML ARS cluster reconstituted the pause site, as did multiple copies of DNA elements (A and B1) that bind ORC. The orc2-1 mutation, known to alter replication timing at origins, did not detectably affect the pause but activated the silent origin at the HML ARS cluster in a minority of cells. Delaying the time of fork arrival at HML led to the elimination of the pause sites at the HML ARS cluster and at the copy of ARS305 inserted in place of the cluster. Loss of the pause sites was accompanied by activation of the silent origins in the majority of cells. Thus, replication fork movement near HML pauses at a silent origin which is competent for replication initiation but kept silent through Orc2p, a component of the replication initiator. Possible functions for replication fork pause sites in checkpoints, S-phase regulation, mating-type switching, and transcriptionally silent heterochromatin are discussed.

Antitumor drug adozelesin differentially affects active and silent origins of DNA replication in yeast checkpoint kinase mutants

The antitumor drug adozelesin is a potent cytotoxic DNA-damaging agent. Here we determined how adozelesin affects chromosomal DNA replication at a molecular level in a yeast model system and examined the influence of checkpoint kinase genes, the human homologues of which are mutated in cancer. Analysis of replication intermediates using two-dimensional gel electrophoresis showed that adozelesin inhibited the activity of a replication origin and stalled replication fork progression through chromosomal DNA at the origin. RAD53 and MEC1 protein kinase genes, homologues of human CHK2 and ATM, respectively, regulate an intra-S-phase DNA damage checkpoint and, when mutated, permit unchecked replication of damaged DNA in S-phase. Mutations in these genes did not abrogate adozelesin-induced inhibition of origin activity and fork progression at the replication origin. However, novel replication intermediates indicative of DNA breaks were detected only in the rad53 mutant, suggesting a role for the wild-type gene in maintaining chromosome integrity in the presence of the drug. In contrast to the inhibition of the active replication origin by adozelesin, normally silent origins present in the same chromosome were activated by adozelesin in rad53 and mec1 mutant cells. Thus, an antitumor drug that damages DNA can induce an abnormal replication pattern in a chromosome by activating silent origins, depending upon defects in yeast checkpoint kinase genes, the homologues of which are mutated in cancer. Implications of an abnormal replication pattern for the epigenetic regulation of gene expression are discussed.

Purification, cloning, and characterization of the CEL I nuclease

CEL I, isolated from celery, is the first eukaryotic nuclease known that cleaves DNA with high specificity at sites of base-substitution mismatch and DNA distortion. The enzyme requires Mg(2+) and Zn(2+) for activity, with a pH optimum at neutral pH. We have purified CEL I 33 000-fold to apparent homogeneity. A key improvement is the use of alpha-methyl-mannoside in the purification buffers to overcome the aggregation of glycoproteins with endogenous lectins. The SDS gel electrophoresis band for the homogeneous CEL I, with and without the removal of its carbohydrate moieties, was extracted, renatured, and shown to have mismatch cutting specificity. After determination of the amino acid sequence of 28% of the CEL I polypeptide, we cloned the CEL I cDNA. Potential orthologs are nucleases putatively encoded by the genes BFN1 of Arabidopsis, ZEN1 of Zinnia, and DSA6 of daylily. Homologies of CEL I with S1 and P1 nucleases are much lower. We propose that CEL I exemplifies a new family of neutral pH optimum, magnesium-stimulated, mismatch duplex-recognizing nucleases, within the S1 superfamily.

The inefficient replication origin from yeast ribosomal DNA is naturally impaired in the ARS consensus sequence and in DNA unwinding

Ribosomal DNA (rDNA) replication origins of Saccharomyces cerevisiae are known to function inefficiently, both in the context of the tandem rDNA repeats in the chromosome and as single copy autonomously replicating sequences (ARSs) in plasmids. Here we examined components of the rDNA ARS that might contribute to inefficient extrachromosomal replication. Like the efficient H4 ARS, the rDNA ARS requires a match to the 11 bp ARS consensus sequence (ACS) and a broad non-conserved region that may contain multiple elements, including a DNA unwinding element (DUE). Using a single-strand-specific nuclease hypersensitivity assay and by determining the superhelical density required for stable DNA unwinding, we found that the DNA of the rDNA ARS is not as easily unwound as the H4 ARS. Unwinding of the rDNA ARS required additional energy, similar to the unwinding of mutations in the H4 ARS that stabilize the double helix in the DUE region and impair replication. In vivo extrachromosomal replication of the rDNA ARS was cold sensitive, like H4 ARS mutants that require additional energy to unwind the DUE region but unlike the easily unwound, wild-type H4 ARS. Impairment of replication function at reduced temperature suggests that the elevated energy requirement for DNA unwinding inherent in the wild-type rDNA ARS contributes to inefficient replication function. We also examined the essential ACS match in the rDNA ARS, which is known to be imperfect at one position. A point mutation in the essential ACS that corrects the imperfect match increased the efficiency of extrachromosomal replication. Our results reveal that the essential ACS element and DNA unwinding in the rDNA ARS are naturally impaired, suggesting that inefficient function of the rDNA replication origin has a biological purpose.

Activation of silent replication origins at autonomously replicating sequence elements near the HML locus in budding yeast

In the budding yeast, Saccharomyces cerevisiae, replicators can function outside the chromosome as autonomously replicating sequence (ARS) elements; however, within chromosome III, certain ARSs near the transcriptionally silent HML locus show no replication origin activity. Two of these ARSs comprise the transcriptional silencers E (ARS301) and I (ARS302). Another, ARS303, resides between HML and the CHA1 gene, and its function is not known. Here we further localized and characterized ARS303 and in the process discovered a new ARS, ARS320. Both ARS303 and ARS320 are competent as chromosomal replication origins since origin activity was seen when they were inserted at a different position in chromosome III. However, at their native locations, where the two ARSs are in a cluster with ARS302, the I silencer, no replication origin activity was detected regardless of yeast mating type, special growth conditions that induce the transcriptionally repressed CHA1 gene, trans-acting mutations that abrogate transcriptional silencing at HML (sir3, orc5), or cis-acting mutations that delete the E and I silencers containing ARS elements. These results suggest that, for the HML ARS cluster (ARS303, ARS320, and ARS302), inactivity of origins is independent of local transcriptional silencing, even though origins and silencers share key cis- and trans-acting components. Surprisingly, deletion of active replication origins located 25 kb (ORI305) and 59 kb (ORI306) away led to detection of replication origin function at the HML ARS cluster, as well as at ARS301, the E silencer. Thus, replication origin silencing at HML ARSs is mediated by active replication origins residing at long distances from HML in the chromosome. The distal active origins are known to fire early in S phase, and we propose that their inactivation delays replication fork arrival at HML, providing additional time for HML ARSs to fire as origins.

Functional equivalency and diversity of cis-acting elements among yeast replication origins

The DNA replication origins of the yeast Saccharomyces cerevisiae require several short functional elements, most of which are not conserved in sequence. To better characterize ARS305, a replicator from a chromosomal origin, we swapped functional DNA elements of ARS305 with defined elements of ARS1. ARS305 contains elements that are functionally exchangeable with ARS1 A and B1 elements, which are known to bind the origin recognition complex; however, the ARS1 A element differs in that it does not require a 3' box adjacent to the essential autonomously replicating sequence consensus. At the position corresponding to ARS1 B3, ARS305 has a novel element, B4, that can functionally substitute for every type of short element (B1, B2, and B3) in the B domain. Unexpectedly, the replacement of element B4 by ARS1 B3, which binds ABF1p and is known as a replication enhancer, inhibited ARS305 function. ARS305 has no short functional element at or near positions corresponding to the B2 elements in ARS1 and ARS307 but contains an easily unwound region whose functional importance was supported by a broad G+C-rich substitution mutation. Surprisingly, the easily unwound region can functionally substitute for the ARS1 B2 element, even though ARS1 B2 was found to possess a distinct DNA sequence requirement. The functionally conserved B2 element in ARS307 contains a known sequence requirement, and helical stability analysis of linker and minilinker mutations suggested that B2 also contains a DNA unwinding element (DUE). Our findings suggest that yeast replication origins employ a B2 element or a DUE to mediate a common function, DNA unwinding during initiation, although not necessarily through a common mechanism.

Bone registration method for robot assisted surgery: pedicle screw insertion

A registration method that identifies bone geometry with respect to a robotic manipulator arm is presented. Although the method is generally applicable to many orthopaedic internal fixation procedures, it was only demonstrated for the insertion of pedicle screws in vertebral bodies for spine fixation. The method relies upon obtaining an impression of the vertebral bodies. Computerized tomography (CT) scans of both vertebrae and mould are reconstructed using a computer aided engineering (CAE) system. From the reconstructions, the surgeon is able to do preoperative planning including selection of pedicle screw diameter, direction of screw through pedicle, point of entry and length of engagement. The three-dimensional models are than meshed to determine positions of the surgeon's preoperative plan relative to the mould. Intra-operative positions are defined in space by a mechanical fixture rigidly attached to the mould and designed to allow a manipulator end-effector to recognize the global coordinates of the in vivo spine. The theory and methodology were validated using a five-axis manipulator arm. This initial presentation assumes and allows no relative motion between vertebrae in vivo.

Factors affecting the pullout strength of cancellous bone screws

Screws placed into cancellous bone in orthopedic surgical applications, such as fixation of fractures of the femoral neck or the lumbar spine, can be subjected to high loads. Screw pullout is a possibility, especially if low density osteoporotic bone is encountered. The overall goal of this study was to determine how screw thread geometry, tapping, and cannulation affect the holding power of screws in cancellous bone and determine whether current designs achieve maximum purchase strength. Twelve types of commercially available cannulated and noncannulated cancellous bone screws were tested for pullout strength in rigid unicellular polyurethane foams of apparent densities and shear strengths within the range reported for human cancellous bone. The experimentally derived pullout strength was compared to a predicted shear failure force of the internal threads formed in the polyurethane foam. Screws embedded in porous materials pullout by shearing the internal threads in the porous material. Experimental pullout force was highly correlated to the predicted shear failure force (slope = 1.05, R2 = 0.947) demonstrating that it is controlled by the major diameter of the screw, the length of engagement of the thread, the shear strength of the material into which the screw is embedded, and a thread shape factor (TSF) which accounts for screw thread depth and pitch. The average TSF for cannulated screws was 17 percent lower than that of noncannulated cancellous screws, and the pullout force was correspondingly less. Increasing the TSF, a result of decreasing thread pitch or increasing thread depth, increases screw purchase strength in porous materials. Tapping was found to reduce pullout force by an average of 8 percent compared with nontapped holes (p = 0.0001). Tapping in porous materials decreases screw pullout strength because the removal of material by the tap enlarges hole volume by an average of 27 percent, in effect decreasing the depth and shear area of the internal threads in the porous material.

Multiple DNA elements in ARS305 determine replication origin activity in a yeast chromosome

A yeast autonomously replicating sequence, ARS305, shares essential components with a chromosome III replicator, ORI305. Known components include an ARS consensus sequence (ACS) element, presumed to bind the origin recognition complex (ORC), and a broad 3'-flanking sequence which contains a DNA unwinding element. Here linker substitution mutagenesis of ARS305 and analysis of plasmid mitotic stability identified three short sequence elements within the broad 3'-flanking sequence. The major functional element resides directly 3' of the ACS and the two remaining elements reside further downstream, all within non-conserved ARS sequences. To determine the contribution of the elements to replication origin function in the chromosome, selected linker mutations were transplaced into the ORI305 locus and two-dimensional gel electrophoresis was used to analyze replication bubble formation and fork directions. Mutation of the major functional element identified in the plasmid mitotic stability assay inactivated replication origin function in the chromosome. Mutation of each of the two remaining elements diminished both plasmid ARS and chromosomal origin activities to similar levels. Thus multiple DNA elements identified in the plasmid ARS are determinants of replication origin function in the natural context of the chromosome. Comparison with two other genetically defined chromosomal replicators reveals a conservation of functional elements known to bind ORC, but no two replicators are identical in the arrangement of elements downstream of ORC binding elements or in the extent of functional sequences adjacent to the ACS.

[Level of atrial natriuretic peptide (ANP) in plasma of patients with chronic renal failure during hemodialysis]

Two groups of subjects (uraemic and control) were studied. The group A consisted of 20 patients treated by HD (haemodialysis). The mean age was x +/- SD--36.6 +/- 7.3 years, duration of haemodialysis treatment 32.8 +/- 7.7 months, cuprophan dialyzers and acetate containing solution--35 mEq/l--were used, time of HD--4 hours 3 times weekly, predialysis serum creatinine was 876 +/- 189 mumol/l (9.8 +/- 2.1 mg%). This group of patients was subdivided in two groups. The group I comprised 9 patients with hypotensive episodes that occurred during HD (systolic blood pressure < 90 mmHg), and the group II comprised 11 patients without hypotensive episodes. The control group comprised 20 healthy subjects (mean age 36.7 +/- 12.1 years, serum creatinine level 77 +/- 16 mumol/l (0.9 +/- 0.2 mg%). In all examined subjects the following experimental protocol was used. Blood pressure (BP) was determined at about 8 a.m. after an overnight rest. Then blood samples were withdrawn for estimation of ANP, haematocrit value (Ht), haemoglobin (Hb) and creatinine concentrations. Between 8 and 12 a.m. all examined uraemic subjects were dialyzed. After each hour of dialysis BP was measured and blood samples were taken. ANP (Peninsula Lab.Kids.) was measured using RIA method, and other biochemical parameters using routine methods. Serum creatinine and plasma ANP levels significantly decreased after HD. No significant differences were seen between the both uraemic groups. No significant correlations between systolic blood pressure, ANP level in examined group were observed.

CONCLUSIONS

1. In all uraemic subjects, plasma ANP level was significantly higher than in control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased concentration of beta-endorphin in the sera of patients with severe atopic dermatitis

Serum beta-endorphin was measured by radioimmunoassay in 25 patients with atopic dermatitis and 100 healthy subjects. The neuropeptide was found to be markedly (p < 0.001) increased in patients with atopic dermatitis (9.2 +/- 3.4 pg/ml) as compared to normal controls (6.1 +/- 1.5 pg/ml). A correlation between increased serum beta-endorphin concentration and some clinical parameters of the disease has been found. The statistically significant elevation of beta-endorphin was found in patients with widespread atopic dermatitis lesions involving more than 20% of the skin surface (11.1 +/- 3.6 pg/ml), a high disease severity score (10.7 +/- 3.7 pg/ml), and previous bronchial asthma symptoms (11.6 +/- 3.1 pg/ml). A possible explanation of increased beta-endorphin is either its generation in atopic dermatitis lesions by inflammatory cells or activation of pituitary-adrenal axis by psychoneural factors in the mechanism of chronic stress.

Multi-centre comparison of ABBOTT MATRIX Aero to Pharmacia Standard RAST, Modified RAST and skin puncture tests

ABBOTT MATRIX Aero is an enzyme immunoassay which measures specific IgE antibodies to 14 individually calibrated airborne allergens using a single serum specimen. In this study, ABBOTT MATRIX performance was evaluated in comparison to the results of skin puncture test and the Standard and Modified RAST procedures. The ABBOTT MATRIX demonstrated overall sensitivity of 89% vs. Standard RAST and Modified RAST, with specificity greater than 92% vs. both methods. ABBOTT MATRIX sensitivity vs. skin test (71%) exceeded that of the Standard and Modified RAST procedures (62% and 67% respectively). Positive results reported by ABBOTT MATRIX but not RAST were corroborated by skin test results for 3 of 5 allergens evaluated. All in vitro systems demonstrated specificity of approximately 90% vs. skin test. The ABBOTT MATRIX system provided results which compared favorably with the results of skin test and RAST, but required less hands-on time to obtain quantitative specific IgE measurements to multiple allergens.

Increased concentration of beta-endorphin in sera of patients with psoriasis and other inflammatory dermatoses

Serum beta-endorphin was quantified by radioimmunoassay in 71 patients with psoriasis vulgaris, other chronic inflammatory skin diseases with T-cell infiltrates [atopic dermatitis (n = 25), and systemic sclerosis (n = 34)], and 100 healthy subjects. The neuropeptide was found to be markedly (P < 0.001) increased in patients with psoriasis (14.4 pg/ml), atopic dermatitis (9.2 pg/ml) and systemic sclerosis (9.8 pg/ml) compared with normal controls (6.1 pg/ml). The highest values of beta-endorphin were found in patients with actively spreading plaque psoriasis (17.3 pg/ml), whereas lesion-free patients showed a reduction in neuropeptide concentration (10.2 pg/ml). The levels were much higher in patients with widespread psoriatic lesions (> 60% body surface; 16.2 pg/ml), which lasted longer than 3 months (15.8 pg/ml), whereas neither the presence of stress nor itching correlated with the serum peptide concentration. Our data suggest that beta-endorphin is produced in psoriatic lesions by inflammatory cells, rather than the increased levels being the result of activation of the pituitary-adrenal axis by chronic stress. The generation of neuropeptide in psoriatic lesions and its antinociceptive effect on the peripheral sensory nerves might explain why pruritus is a relatively rare phenomenon in psoriasis.

Neuropeptides in psoriasis: possible role of beta-endorphin in the pathomechanism of the disease

BACKGROUND

An increased concentration of neuropeptides in psoriatic lesional skin may be responsible for alterations in the neurogenic erythematous response and transmission of stimuli through sensory nerve fibers (sensation of pruritus).

METHODS

Increasing doses of capsaicin from 0.125 to 4 micrograms/cm2 were applied to nonlesional psoriatic skin to establish the minimal dose that induced the substance P-mediated neurogenic response in 30 patients with psoriasis. Plasma beta-endorphin was quantitated in 71 psoriatics by radioimmunoassay using NEN 1251-RIA kit.

RESULTS

The mean beta-endorphin concentration was increased about 2-fold compared to normals, whereas doses of capsaicin needed to induce erythema were higher (1-4 micrograms/cm2) in psoriatics (mainly in patients with type II psoriasis) than in healthy subjects (0.125-0.25 microgram/cm2).

CONCLUSIONS

The data indicate that increased beta-endorphin in psoriatic skin might affect both substance P-mediated neurogenic inflammation and transmission of sensory stimuli due to local antinociceptive effects of this opioid. The differences in the neurogenic response in type I and II psoriasis may be related to the degradation of substance P and beta-endorphin by neutral proteinases in the lesional skin.

[Level of endothelin-1 and 2 in plasma of patients with chronic renal failure]

The aim of the study was to answer 3 questions: 1. does plasma endothelin level differ in patients with chronic renal failure from that of healthy subjects. 2. does plasma endothelin level differ in patients with chronic renal failure treated with haemodialysis from those treated without dialysis. 3. does plasma endothelin level change during haemodialysis. 63 patients with chronic renal failure (pnn, 23 treated without dialyses and 40 with dialyses) as well as 20 healthy subjects were studied. Plasma endothelin and creatinine were estimated under basal conditions and in the dialysed patients--immediately after dialysis. Plasma endothelin level was higher in patients with pnn than in normals, regardless to dialysotherapy. It rose after dialysis. Plasma creatinine fell after dialysis. Positive significant correlation was found between the levels of creatinine and endothelin in the whole group studied.

DNA helical instability facilitates initiation at the SV40 replication origin

Previous analysis of mutations in bacterial and yeast replication origins has identified a genetic component, termed a DNA unwinding element (DUE), whose intrinsic helical instability is essential for origin function. For the SV40 replication origin, we show here that the early palindrome (EP) and A + T-rich (AT) domains both exhibit helical instability, despite their dissimilar A + T compositions. To test the possible contribution of helical instability to SV40 origin function, the relationship between helical stability of mutant origin sequences and their known origin activity in vitro and in vivo was examined. Origin activity correlates inversely with the helical stability of mutations within the EP domain but not the AT domain or the T-antigen binding domain. The quantitative correlation holds for four different measures of origin activity determined in vitro and in vivo. An even better-correlated collection of mutations was found in a specific portion of the EP domain. This specific EP subdomain coincides with the sequence known to be strand-separated after T-antigen binds the origin in vitro and with the origin of bidirectional replication in vivo. Our analysis of origin mutations indicates that the helical instability of the specific EP subdomain is required to facilitate T-antigen-induced melting and the initiation of DNA replication. The sensitivity of the required EP subdomain to mutations that stabilize the DNA helix defines the DUE of the SV40 replication origin.

A DNA unwinding element and an ARS consensus comprise a replication origin within a yeast chromosome

We have defined a replication origin, ORI305, within chromosome III of Saccharomyces cerevisiae by means of mutational analysis. cis-acting elements required for origin activity in the chromosome, as assayed by two-dimensional gel electrophoresis of replication intermediates, are the same as those required for the function of an autonomously replicating sequence, ARS305, in a plasmid. Essential elements include (i) an 11 bp sequence that is a near match to the ARS consensus and (ii) a broad sequence directly 3' to the consensus near match. Origin function is inactivated by point mutations in the essential near match sequence, suggesting that the sequence contributes to specifying the origin in the chromosome. Other consensus near matches with different sequences are present but are not required. The essential 3'-flanking sequence exhibits DNA helical instability and is sensitive to deletion mutations that stabilize the DNA helix. The wild-type 3'-flanking sequence can be functionally substituted by dissimilar sequences that also exhibit helical instability. The requirement for DNA helical instability indicates that the essential 3'-flanking sequence serves as a DNA unwinding element in the chromosome.

[Levels of endothelin and atrial natriuretic peptide (ANP) in plasma of patients with chronic renal failure treated by hemodialysis]

Two groups of subjects were studied. The group A consisted of 40 patients treated by HD (haemodialysis) (mean age--x +/- SEM 38.6 +/- 1.47 years, duration of haemodialysis treatment 36.8 +/- 3.7 months, cuprophan dialyzers and acetate containing solution--38 mEg/l--were used, time of HD--4 hours 3 times weekly, predialysis serum creatinine was 900.8 +/- 32.1 mumol/l (10.2 +/- 0.4 mg%) postdialysis serum creatinine was 467.8 +/- 28.3 mumol/l (5.3 +/- 0.3 mg%). Patients were not treated with erythropoietin. The control group comprised 20 healthy subjects (mean age 36.7 +/- 2.7 years and serum creatinine level 76.7 +/- 3.5 mumol/l (0.9 +/- 0.1 mg%). In all examined subjects the following experimental protocol was used. In both group blood pressure (BP) and heart rate (HR) were determined at about 8 a.m. after an overnight rest. Then blood samples were withdrawn for estimation of ANP, endothelin, haematocrit value (Ht), haemoglobin (Hb) and creatinine concentrations. Between 8 and 12 a.m. all examined subjects of the group A were dialysed. After each hour of dialysis BP and HR were measured and blood samples were withdrawn ANP (Peninsula Lab.Kids.) and endothelin (Amersham Kids) were measured using RIA methods, but other biochemical parameters using routine methods. Serum creatinine and plasma ANP levels significantly decreased after HD. Plasma endothelin level was significantly higher than in the control subjects. After first hour of HD a significant decrease of plasma endothelin was observed and than plasma endothelin level started to increase. No significant correalations between creatinine, ANP and endothelin levels in examined group was observed.

[Effect of hemodialysis on left ventricular function in patients with chronic renal failure assessment with radionuclide ventriculography]

To examine the effects of haemodialysis (HD) on left ventricular (LV) function, gated radionuclide ventriculography was conducted before and after HD in 16 patients with chronic renal failure (CRF) and in 12 healthy persons. The LV sectorial function was assessed by subdividing the LV region of interest into 6 sectors. Global ejection fraction (EF) was unchanged by dialysis (61.4 +/- 8.3% before vs. 63.5 +/- 10.4% after) (mean +/- S.D.). EF of sectors 4 and 5 was improved significantly (69.3 +/- 10.7% and 85.6 +/- 17.1% before vs. 81.7 +/- 18.4% and 97.4 +/- 22.0% after) (p < 0.05 and p < 0.05). The peak ejection rate (PER) was increased following HD (3.07 +/- 1.03 EDc/s before vs. 3.88 +/- 0.88 EDc/s after) (p < 0.02). The time to end systole (TES) corrected for R-R interval was unchanged by HD (46.3 +/- 6.3 before vs. 43.8 +/- 5.3 after). The peak filling rate (PFR) was unchanged by HD (3.41 +/- 0.77 EDc/s before vs. 3.05 +/- 0.45 EDc/s after). The time to peak filling rate (TPFR) corrected for R-R interval was increased (21.8 +/- 5.3 before vs 25.9 +/- 5.0 after) (p < 0.02). This study indicates that HD produces beneficial effects on LV systolic function in CRF patients and does not improve LV filling in early diastole.

cis-acting components in the replication origin from ribosomal DNA of Saccharomyces cerevisiae

The ribosomal DNA (rDNA) repeats of Saccharomyces cerevisiae contain an autonomously replicating sequence (ARS) that colocalizes with a chromosomal origin of replication. We show that a minimal sequence necessary for full ARS function corresponds to a 107-bp rDNA fragment which contains three 10-of-11-bp matches to the ARS consensus sequence. Point mutations in only one of the 10-of-11-bp matches, GTTTAT GTTTT, inactivate the rDNA ARS, indicating that this consensus sequence is essential. A perfect match to a revised ARS consensus is present but not essential. Sequences up to 9 bp 5' from the essential consensus are dispensable. A broad DNA region directly 3' to the essential consensus is required and is easily unwound as indicated by: (i) hypersensitivity to nicking of an approximately 100-bp region by mung bean nuclease in a negatively supercoiled plasmid and (ii) helical instability determined by thermodynamic analysis of the nucleotide sequence. A correlation between DNA helical instability and replication efficiency of wild-type and mutated ribosomal ARS derivatives suggests that a broad region 3' to the essential ARS consensus functions as a DNA unwinding element. Certain point mutations that do not stabilize the DNA helix in the 3' region but reduce ARS efficiency reveal an element distinct from, but overlapping, the DNA unwinding element. The nucleotide sequence of the functionally important constituents in the ARS appears to be conserved among the rDNA repeats in the chromosome.

Easily unwound DNA sequences and hairpin structures in the Epstein-Barr virus origin of plasmid replication

The Epstein-Barr virus (EBV) origin of plasmid replication (oriP) includes two known cis-acting components, the dyad symmetry region and the family of repeats. We used P1 nuclease, a single-strand-specific endonuclease, to probe EBV oriP for DNA sequences that are intrinsically easy to unwind on a negatively supercoiled plasmid. Selective nuclease hypersensitivity was detected in the family of repeats on an oriP-containing plasmid and in the dyad symmetry region on a plasmid that lacks the family of repeats, indicating that the DNA in both cis-acting components is intrinsically easy to unwind. The hierarchy of nuclease hypersensitivity indicates that the family of repeats is more easily unwound than the dyad symmetry region, consistent with the hierarchy of helical stability predicted by computer analysis of the DNA sequence. A specific subset of the family of repeats is nuclease hypersensitive, and the DNA structure deduced from nucleotide-level analysis of the P1 nuclease nicks is a cruciform near a single-stranded bubble. The dyad symmetry region unwinds to form a broad single-stranded bubble containing hairpins in the 65-bp dyad sequence. We propose that the intrinsic ease of unwinding the dyad symmetry region, the actual origin of DNA replication, is an important component in the mechanism of initiation.

[Effect of hemodialysis on levels of parathormone in blood of patients with chronic kidney failure]

In 28 patients with chronic renal failure the concentration was determined of "MID"-"carboxyterminal" PTH fragment (M/C-PTH) and of beta-2-microglobulin in the serum during haemodialysis. It was found that the serum M/C-PTH concentration was increased significantly during haemodialysis using Cuprophane dialysers. The serum concentrations of M/C-PTH and beta-2-microglobulin were not changing significantly during the first hour of haemodialysis. The authors believe that the increase of serum M/C-PTH concentration during haemodialysis may be due to unsatisfactory biocompatibility of Cuprophane dialyzing membranes.

[Effect of many years of hemodialysis therapy on FSH secretion induced by luliberin in men with chronic renal failure]

The purpose of the work was an explanation, what was the influence of many years of hemodialysis therapy on FSH secretion in men with chronic renal failure (CRF). The studies were carried out in 41 men with CRF treated with haemodialysis, 10 men with advanced CRF who were not dialysed, and in 15 healthy men. In all studied individuals the luliberin stimulation test (LH-RH) was performed. It was found that men with CRF, independently of the duration of hemodialysis therapy, were characterized by increased serum FSH concentration in comparison to healthy subjects. In men dialysed form over 50 months, the FSH concentration was higher than in those dialysed for a shorter time period, and not dialysed. The reaction of FSH secretion stimulated by LH-RH in men dialysed for less than 100 months and not dialysed was diminished while in those dialysed for over 100 months it was normalized.

Ease of DNA unwinding is a conserved property of yeast replication origins

Autonomously replicating sequence (ARS) elements function as plasmid replication origins. Our studies of the H4 ARS and ARS307 have established the requirement for a DNA unwinding element (DUE), a broad easily-unwound sequence 3' to the essential consensus that likely facilitates opening of the origin. In this report, we examine the intrinsic ease of unwinding a variety of ARS elements using (1) a single-strand-specific nuclease to probe for DNA unwinding in a negatively-supercoiled plasmid, and (2) a computer program that calculates DNA helical stability from the nucleotide sequence. ARS elements that are associated with replication origins on chromosome III are nuclease hypersensitive, and the helical stability minima correctly predict the location and hierarchy of the hypersensitive sites. All well-studied ARS elements in which the essential consensus sequence has been identified by mutational analysis contain a 100-bp region of low helical stability immediately 3' to the consensus, as do ARS elements created by mutation within the prokaryotic M13 vector. The level of helical stability is, in all cases, below that of ARS307 derivatives inactivated by mutations in the DUE. Our findings indicate that the ease of DNA unwinding at the broad region directly 3' to the ARS consensus is a conserved property of yeast replication origins.