The single helix in protein L is largely disrupted at the rate-limiting step in folding

To investigate the role of helix formation in the folding of protein L, a 62 residue alpha/beta protein, we studied the consequences of both single and multiple mutations in the helix on the kinetics of folding. A triple mutant with 11 additional carbon atoms in core residues in the amino-terminal portion of the helix folded substantially faster than wild type, suggesting that hydrophobic association with residues elsewhere in the protein occurs at the rate-limiting step in folding. However, helix-destabilizing mutations had little effect on the rate of folding; in particular, a triple glycine substitution on the solvent-exposed side of the helix increased the unfolding rate 56-fold while reducing the folding rate less than threefold. Thus, in contrast to the predictions of models of folding involving the coalescence of well-formed secondary structure elements, the single helix in protein L appears to be largely disrupted at the rate-limiting step in folding and unfolding.     

The clinical assessment of cancer tests: a statistical approach to the prediction of "false positive" rates from controls

As the sensitivity of the new in vitro cancer detection techniques increases, a larger number of "false positive" results can be expected from control populations apparently free from malignant disease at the time of the test. An attempt is made to predict the number of unexplained positives, together with the expected age and sex distribution, using published cancer registration statistics. The predicted numbers are compared with the observed numbers of unexplained positives in two clinical trials of the MEM test.     

The impact of candidemia on length of hospital stay, outcome, and overall cost of illness

Although numerous studies have examined trends in nosocomial fungal infections, few have specifically addressed the cost of care associated with candidemia. This study analyzes the direct medical costs associated with treating candidemia in the United States. The study design was a cost-of-illness analysis estimating the average cost of candidemia for a single episode of care. Data were obtained from three sources: the 1993 Healthcare Cost and Utilization Project of the Agency for Health Care Policy and Research, the relevant literature, and a clinical expert in systemic fungal infections. The estimated cost (1997 U.S.$) of an episode of care for candidemia is $34,123 per Medicare patient and $44,536 per private insurance patient. The major cost associated with candidemia is that of an increased hospital stay. The estimated cost of care for candidemia may change in the future because of the use of more expensive antifungal treatments with improved safety and efficacy profiles.     

Folding rate dependence on the chain length of RNA-like heteropolymers

BACKGROUND: Economical studies on surgery of intracranial aneurysms have considered only the significant benefit of surgical approach on unruptured aneurysms and no studies have been performed comparing cost/benefit analysis of early vs delayed surgery. The present study was retrospectively performed in order to verify whether different treatment options in aneurysm surgery have a different cost/benefit ratio. METHODS: We have analysed a series of 137 patients which underwent surgery for intracranial aneurysms (21 unruptured aneurysms, 56 early surgery and 60 delayed surgery). In the analysis we assumed that each state of an operated patient has an assigned quality of life value and an associated medical cost. We expressed the outcome of each patient as the expected length of survival adjusted for quality, and referred to it as "quality-adjusted life years" (QALY). We considered for each patient the direct cost of Hospitalisation (obtained from DRG reimbursement), the Rehabilitation cost and the correction due to QALY adjusted for age and deficit. RESULTS: Significantly higher costs are reported in patients which present as major complication the hydrocephalus and which are treated with nimodipine; moreover, the costs for patients operated for unruptured aneurysms is significantly lower than that of patients which presented with SAH. Meanwhile, the average QALY adjusted for post-operative neurological deficit at three months follow-up is higher in patients operated for unruptured aneurysms than in patients operated after SAH. The cost-effectiveness of different treatment strategies did not significantly differ considering age and neurological deficit adjustment; thus, after SAH, the choice of early or delayed surgery may depend on clinical and logistic conditions related to the neurosurgical department and its organisation, because there is no significant economical advantage leading to recommend early versus delayed surgery. CONCLUSIONS: In conclusion the present data suggest that a decreased length of hospitalisation and a decreased cost for treatment of unruptured aneurysms should justify a more rigorous preventive screening with available non invasive neuroimaging techniques.     

认真贯彻产业政策 全面提高钢铁行业竞争力--解读《钢铁产业发展政策》

我国钢铁工业的发展历来受到各界的关心,特别是在固定资产投资增长过快时,钢铁工业更是备受关注.从亚洲金融危机以来,我国实施积极的财政政策拉动内需,在拉动国民经济发展的三驾马车中,与消费和出口相比,首先能够快速启动国民经济增长的就是增加固定资产投资.我国国民经济经过近10年的又一轮快速增长,固定资产投资领域出现了一些过热现象.在经济波动和国家宏观调控的过程中,我国钢铁工业也经历着一次又一次的涨落起伏.     

New features of 23S ribosomal RNA folding: the long helix 41-42 makes a "U-turn" inside the ribosome

23S rRNA from Escherichia coli was cleaved at single internucleotide bonds using ribonuclease H in the presence of appropriate chimeric oligonucleotides; the individual cleavage sites were between residues 384 and 385, 867 and 868, 1045 and 1046, and 2510 and 2511, with an additional fortuitous cleavage at positions 1117 and 1118. In each case, the 3' terminus of the 5' fragment was ligated to radioactively labeled 4-thiouridine 5'-,3'-biphosphate ("psUp"), and the cleaved 23S rRNA carrying this label was reconstituted into 50S subunits. The 50S subunits were able to associate normally with 30S subunits to form 70S ribosomes. Intra-RNA crosslinks from the 4-thiouridine residues were induced by irradiation at 350 nm, and the crosslink sites within the 23S rRNA were analyzed. The rRNA molecules carrying psUp at positions 867 and 1117 showed crosslinks to nearby positions on the opposite strand of the same double helix where the cleavage was located, and no crosslinking was detected from position 2510. In contrast, the rRNA carrying psUp at position 384 showed crosslinking to nt 420 (and sometimes also to 416 and 425) in the neighboring helix in 23S rRNA, and the rRNA with psUp at position 1045 gave a crosslink to residue 993. The latter crosslink demonstrates that the long helix 41-42 of the 23S rRNA (which carries the region associated with GTPase activity) must double back on itself, forming a "U-turn" in the ribosome. This result is discussed in terms of the topography of the GTPase region in the 50S subunit, and its relation to the locations of the 5S rRNA and the peptidyl transferase center.     

Fast folding mutants of the Tetrahymena group I ribozyme reveal a rugged folding energy landscape

A model for the kinetic folding pathway of the Tetrahymena ribozyme has been proposed where the two main structural domains, P4-P6 and P3-P7, form in a hierarchical manner with P4-P6 forming first and P3-P7 folding on the minute timescale. Recent studies in our laboratory identified a set of mutations that accelerate P3-P7 formation, and all of these mutations appear to destabilize a native-like kinetic trap. To better understand the microscopic details of this slow step in the Tetrahymena ribozyme folding pathway, we have used a previously developed kinetic oligonucleotide hybridization assay to characterize the folding of several fast folding mutants. A comparison of the temperature dependence of P3-P7 folding between the mutant and wild-type ribozymes demonstrates that a majority of the mutations act by decreasing the activation enthalpy required to reach the transition state and supports the existence of the native-like kinetic trap. In several mutant ribozymes, P3-P7 folds with biphasic kinetics, indicating that only a subpopulation of molecules can evade the kinetic barrier. The rate of folding of the wild-type increases in the presence of urea, while for the mutants urea merely shifts the distribution between the two folding populations. Small structural changes or changes in solvent can accelerate folding, but these changes lead to complex folding behavior, and do not give rise to rapid two-state folding transitions. These results support the recent view of folding as an ensemble of molecules traversing a rugged energy landscape to reach the lowest energy state.     

The folding process of hen lysozyme: a perspective from the ''new view''

Shuttle mutagenesis using signature-tagged transposons was employed to generate a library of individually tagged mutants of the Neisseria meningitidis strain B1940, which belongs to serogroup B. The use of tagged transposons allowed us to monitor for enrichment for single mutants during the process of shuttle mutagenesis, by amplification of the tags and subsequent sequence determination. Enrichment of a single clone occurred during the transformation of the meningococci with transposon-containing plasmid DNA. Sequence determination around the site of transposon insertion revealed that the transposon had mutagenized a previously unknown locus, which was designated hrtA (high rate of transformation). hrtA-mediated transformation was independent of TnMax5 and tag sequences, and it most probably involved recombination events. The hrtA locus is restricted to meningococci and gonococci and is present in few apathogenic neisserial species. Chromosomal mapping of hrtA and six further hrt sites revealed a random distribution of highly transforming DNA fragments on the meningococcal chromosome. In conclusion, our data demonstrate that shuttle mutagenesis of naturally competent bacteria using signature-tagged transposons allows the isolation of chromosomal DNA fragments, which exhibit a high transformation efficiency, and which, therefore, are likely to be involved in horizontal gene transfer.     

Effect of a "chunked" typography on reading rate and comprehension.

3 studies with 104 undergraduates investigated the effect of a chunked typography on the reading rate and comprehension of mature readers, reading at their normal rates. Passages and questions from a standardized reading test were displayed via an electromechanical device which allowed actual reading times to be recorded. 5 experimental chunked formats were compared with each other and 1 selected for further study. The chunking of the material was arbitrarily intuitive but a subsequent analysis indicated that the chunked boundaries usually coincided with the major phrase boundaries of immediate constituents. There was no important or statistically significant difference between the experimental chunked format and the control format, either on the reading rate or comprehension measures. Another control format, no punctuation or capitalization, did result in significant decrements in reading rate and comprehension. It is concluded that the spatial separation of reading materials into groups of meaningfully related words does not improve the reading efficiency of mature readers when they are reading at their normal rate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The slow step of folding of Staphylococcus aureus PC1 beta-lactamase involves the collapse of a surface loop rate limited by the trans to cis isomerization of a non-proline peptide bond

We wished to test the hypothesis that the non proline cis to trans isomerization of the peptide bond at position 167 in the S. aureus beta-lactamase PC1 exerts a significant controlling effect on the folding pathway of this enzyme. The previous data presented in support of this hypothesis could not rule out the effect of factors unrelated to non-proline cis/trans isomerization. We have used the plasmid pET9d to direct soluble overproduction of the S. aureus beta-lactamase PC1 and a site-directed mutant (Ile 167 to Pro) in Escherichia coli. Following purification the proteins were subjected to a comparative analysis of the kinetics of unfolding and refolding using the techniques of near- and far-UV circular dichroism spectroscopy and fluorescence spectroscopy in conjunction with "double-jump" experiments. Results show that the fully-unfolded I167P mutant enzyme retains 20% of molecules in a fast-refolding form and that slower-refolding molecules fold faster than the recombinant wild-type enzyme. The final stage of folding involves folding of the omega-loop into a conformation essential for enzymatic activity. In support of the original hypothesis, the folding of this omega-loop is rate limited by the isomerization of the Glu 166-Ile 167 peptide bond.     

The psychology laboratory at the turn of the 20th century.

The author provides a brief history of the psychology laboratory from 1879 to 1900, discusses its crucial role in the founding of scientific psychology, and describes how it enabled psychology's separation from philosophy. The laboratory model is described as a research and graduate training enterprise that operated with K. Danziger's (1990) concept of a "community of scholars" and was eventually extended to the training of undergraduate students. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A single point mutation controls the cholesterol dependence of Semliki Forest virus entry and exit

Hypergastrinaemia-associated changes of non-antral argyrophil cells in man are of increasing interest, because of the development of potent inhibitors of gastric acid secretion. Using an antibody against chromogranin A, we identified micronodular endocrine cell hyperplasia of the oxyntic mucosa in gastric biopsy specimens of patients with hypergastrinaemia of different backgrounds. Consecutive ultrathin sections were examined at the electron-microscopical level. Endocrine cell types within the (extraepithelial) micronodules closely resembled those in the adjacent mucosa. Micronodules were classified into two groups. The first group was composed of endocrine cells only and predominated in patients with drug-induced hypergastrinaemia and/or chronic gastritis, and in a gastrinoma/MEN I patient. The second group represented "neuroendocrine complexes", showing a close intermingling of non-myelinated nerve fibres with endocrine cells, and was found predominantly in pernicious anaemia. Micronodular argyrophil cell growth in man is therefore heterogeneous and depends on the background of the hypergastrinaemia.     

Further evidence that the Hajdu-Cheney syndrome and the "serpentine fibula-polycystic kidney syndrome" are a single entity

The Hajdu-Cheney syndrome (HCS) is a rare autosomal dominant disorder. It comprises a coarse face, short neck, hirsutism, joint laxity, and normal intelligence. Bone dysplasias, include acro-osteolysis, bathrocephaly, and vertebral anomalies. In 1988, Exner [1988: Eur J Pediatr 147:544-546] coined the term "serpentine fibula-polycystic kidney syndrome" (SFPKS) when he reported on a girl with short stature, unusual facial appearance, polycystic kidneys, and elongated curved fibulae. He postulated that it was a new entity different from the Melnick-Needles syndrome. Since his report, five similar cases have been published. Similarities between both HCS and SFPKS were noticed first by us and then by other authors. In this report we show that many clinical and radiological characteristics are shared by the HCS and the SFPKS and hypothesize that they represent a single entity with a variable degree of expression.     

The changing nature of the protein folding transition state: implications for the shape of the free-energy profile for folding

According to landscape theory proteins do not fold by localised pathways, but find their native conformation by a progressive organisation of an ensemble of partly folded structures down a folding funnel. Here, we use kinetics and protein engineering to investigate the shape of the free-energy profile for two-state folding, which is the macroscopic view of the funnel process for small and rapidly folding proteins. Our experiments are based mainly on structural changes of the transition state of chymotrypsin inhibitor 2 (CI2) upon destabilisation with temperature and GdnHCl. The transition state ensemble of CI2 is a localised feature in the free-energy profile that is sharply higher than the other parts of the activation barrier. The relatively fixed position of the CI2 transition state on the reaction coordinate makes it easy to characterise but contributes also to overshadow the rest of the free-energy profile, the shape of which is inaccessible for analysis. Results from mutants of CI2 and comparison with other two-state proteins, however, point at the possibility that the barrier for folding is generally broad and that localised transition states result from minor ripples in the free-energy profile. Accordingly, variabilities in the folding kinetics may not indicate different folding mechanisms, but could be accounted for by various degrees of ruggedness on top of very broad activation barriers for folding. The concept is attractive since it summarises a wide range of folding data which have previously seemed unrelated. It is also supported by theory. Consistent with experiment, broad barriers predict that new transition state ensembles are exposed upon extreme destabilisation or radical mutations.     

Active site mutations in yeast protein disulfide isomerase cause dithiothreitol sensitivity and a reduced rate of protein folding in the endoplasmic reticulum

Aspects of protein disulfide isomerase (PDI) function have been studied in yeast in vivo. PDI contains two thioredoxin-like domains, a and a', each of which contains an active-site CXXC motif. The relative importance of the two domains was analyzed by rendering each one inactive by mutation to SGAS. Such mutations had no significant effect on growth. The domains however, were not equivalent since the rate of folding of carboxypeptidase Y (CPY) in vivo was reduced by inactivation of the a domain but not the a' domain. To investigate the relevance of PDI redox potential, the G and H positions of each CGHC active site were randomly mutagenized. The resulting mutant PDIs were ranked by their growth phenotype on medium containing increasing concentrations of DTT. The rate of CPY folding in the mutants showed the same ranking as the DTT sensitivity, suggesting that the oxidative power of PDI is an important factor in folding in vivo. Mutants with a PDI that cannot perform oxidation reactions on its own (CGHS) had a strongly reduced growth rate. The growth rates, however, did not correlate with CPY folding, suggesting that the protein(s) required for optimal growth are dependent on PDI for oxidation. pdi1-deleted strains overexpressing the yeast PDI homologue EUG1 are viable. Exchanging the wild-type Eug1p C(L/I)HS active site sequences for C(L/I)HC increased the growth rate significantly, however, further highlighting the importance of the oxidizing function for optimal growth.     

Protecting the overall rate of Type I errors for pairwise comparisons with an omnibus test statistic.

Compares 2 procedures for protecting the number of false rejections for a set of all possible pairwise comparisons. The 2-stage strategy of computing pairwise comparisons, conditional on a significant omnibus test, is compared with the multiple comparison strategy that sets a "familywise" critical value directly. The ANOVA test, the Brown and Forsythe test, and the Welch omnibus test, as well as 3 procedures for assessing the significance of pairwise comparisons, are combined into 9 2-stage testing strategies. The data from this study establish that the common strategy of following a significant ANOVA F with Student's t tests on pairs of means results in a substantially inflated rate of Type I error when variances are heterogeneous. Type I error control, however, can be obtained with other 2-stage procedures, and the authors tentatively consider the Welch F″ Welch t″ combination desirable. In addition, the 2 techniques for controlling Type I error do not substantially differ as much as might be expected; some 2-stage procedures are comparable to simultaneous techniques. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)