Intra- and interspecies variation among Bari-1 elements of the melanogaster species group

We have investigated the distribution of sequences homologous to Bari-1, a Tc1-like transposable element first identified in Drosophila melanogaster, in 87 species of the Drosophila genus. We have also isolated and sequenced Bari-1 homologues from D. simulans, D. mauritiana, and D. sechellia, the species constituting with D. melanogaster the melanogaster complex, and from D. diplacantha and D. erecta, two phylogenetically more distant species of the melanogaster group. Within the melanogaster complex the Bari-1 elements are extremely similar to each other, showing nucleotide identity values of at least 99.3%. In contrast, Bari-1-like elements from D. diplacantha and D. erecta are on average only 70% similar to D. melanogaster Bari-1 and are usually defective due to nucleotide deletions and/or insertions in the ORFs encoding their transposases. In D. erecta the defective copies are all located in the chromocenter and on chromosome 4. Surprisingly, while D. melanogaster Bari-1 elements possess 26-bp inverted terminal repeats, their D. diplacantha and D. erecta homologues possess long inverted terminal repeats similar to the terminal structures observed in the S elements of D. melanogaster and in several other Tc1-like elements of different organisms. This finding, together with the nucleotide and amino acid identity level between D. diplacantha and D. erecta elements and Bari-1 of D. melanogaster, suggests a common evolutionary origin and a rapid diversification of the termini of these Drosophila Tc1-like elements.     

Evolution of mammalian apolipoprotein A-I and conservation of antigenicity: correlation with primary and secondary structure

We have evaluated the immunoreactivity of 20 monoclonal antibodies (mAbs) directed against human apolipoprotein (apo)A-I with a panel of high density lipoproteins (HDL) from 13 mammalian species. The pattern of cross-reactivity showed that 20 mAbs had different specificity. While not all mAbs recognized apoA-I from all of the different species, the antigenicity of some sequences was well conserved. Thus, mAb A05 cross-reacted with all species except guinea pig and rat. In contrast, the mAb 4H1, which recognized residues 2-8, required a specific proline in position 3, as no immunoreactivity was found in the species missing this amino acid. Furthermore, the presence of a threonine residue in place of serine (in position 6) in the cynomolgus monkey was associated with a 20-fold loss of immunoreactivity in radioimmunometric assay with 4H1. As most of the epitopes were found in CNBr fragments 2 and 3, we sequenced these regions in four species (horse, goat, sheep, and cat) and analyzed the alignment of most known sequences to evaluate their consensus. Except for the rat and the chicken, considerable identity was observed. This permitted us to deduce the involvement of the residues in some antigenic epitopes. In the middle of apoA-I, a conservative mutation Asp103-->Glu was found sufficient to eliminate all reactivity of this epitope for A11 (residues 99-105 ... 12l6-132) in five species (rabbit, cow, goat, sheep, and rat). The residues essential to the expression of two other epitopes overlapping with A11 were also characterized. Edmundson-wheel representation of 18-residue repeated sequences of the different apoA-I species (for the eight amphipatic helices of residues 46-63, 68-85, 101-118, 123-140, 143-160, 167-184, 189-206, and 222-239) showed that secondary structure of apoA-I was more conserved than the antigenic epitopes. The N-terminal region, residues 1 to about 98, is rich in both strictly preserved sequences and epitope expression in most of the species surveyed. This evolutionary conservation of the N-terminal domain suggests an important yet unknown function.     

Comparative cytologic study of nephron structure in higher vertebrates

A comparative study of the cytological characteristics of the epithelial lining of the nephron and collecting tubules was performed in 9 species of reptiles, 19 species of birds and 12 species of mammals. Representatives of each class of higher vertebrates were shown to have certain specific features of the epithelial lining of different parts of the nephron. Differentiation of various areas of the proximal part of the nephron proceded in phylogeny with different intensity and the maximum specialization was characteristic of the most proximal portion of this part of the nephron. In the cells of the proximal parts of nephrons of some reptiles there were phenomena of apocrine secretion. Evolution of the distal part of the nephron developed to form a loop and differentiation of the distal convoluted segment. The higher differentiation of the epithelial lining of the nephron distal part in birds and mammals, unlike in reptiles, seems to be associated with a more considerable functional specilization of this part. In the cytochemical characteristics of the epithelium of the uriniferous and collecting tubules of kidneys of higher vertebrate animals there are common regularities in the distribution of RNA, proteins and some enzymes. The polysaccharide content is maximum in the epithelial cells of kidneys of reptiles.     

Functional and structural conservation in the mechanosensitive channel MscL implicates elements crucial for mechanosensation

An immortalized cell line (designated MDCT) has been extensively used to investigate the cellular mechanisms of electrolyte transport within the mouse distal convoluted tubule. Mouse distal convoluted tubule cells possess many of the functional characteristics of the in vivo distal convoluted tubule. In the present study, we show that MDCT cells also possess a polyvalent cation-sensing mechanism that is responsive to extracellular magnesium and calcium. Southern hybridization of reverse transcribed-polymerase chain reaction (RT-PCR) products, sequence determination and Western analysis indicated that the calcium-sensing receptor (Casr) is expressed in MDCT cells. Using microfluorescence of single MDCT cells to determine cytosolic Ca2+ signaling, it was shown that the polyvalent cation-sensing mechanism is sensitive to extracellular magnesium concentration ([Mg2+]o) and extracellular calcium concentration ([Ca2+]o) in concentration ranges normally observed in the plasma. Moreover, both [Mg2+]o and [Ca2+]o were effective in generating intracellular Ca2+ transients in the presence of large concentrations of [Ca2+]o and [Mg2+]o, respectively. These responses are unlike those observed for the Casr in the parathyroid gland. Finally, activation of the polycation-sensitive mechanism with either [Mg2+]o or [Ca2+]o inhibited parathyroid hormone-, calcitonin-, glucagon- and arginine vasopressin-stimulated cAMP release in MDCT cells. These studies indicate that immortalized MDCT cells possess a polyvalent cation-sensing mechanism and emphasize the important role this mechanism plays in modulating intracellular signals in response to changes in [Mg2+]o as well as in [Ca2+]o.     

Multiple pathways of reversion in viroids for conservation of structural elements

From site-directed mutagenesis of potato spindle tuber viroid (PSTVd) it had been concluded earlier that the formation of a thermodynamically metastable structure containing hairpin II (HP II) is critical for infectivity. In order to differentiate between structural and sequence effects, in the present work base pairs in HP II were exchanged by site-directed double mutations without significant alterations in the native rod-like structure of PSTVd. The mutants were viable and genetically stable in the first generation, but one of the two mutations reverted to the wild-type nucleotide in the second generation. Single-site mutations in the stem of HP II, which had been described as revertants to the wild-type sequence earlier, were analysed with respect to the time course of reversion and the sequence variation during reversion. All replicating sequence variants were separated by gel electrophoretic techniques and the sequences and their relative frequencies were determined. From both types of studies it can be concluded (i) that HP II is a functional element in the (-)strand replication intermediate, generated due to sequential folding during synthesis, and that it is essential for template activity of (+)strand synthesis; (ii) that G:U pairs are tolerated transiently in (-)strand HP II; the lower stability of such a HP II is compensated by additional mutations outside HP II which suppress the competition of a rod-like structure; and (iii) that the reversions are generated spontaneously during (-)strand synthesis. Furthermore, the double-stranded structure of HP II is the essential element for short term replication of PSTVd but the exact sequence of the wild-type proves to be superior with regard to fitness and replicability of PSTVd.     

A survey of diagnostic practices and the use of epoprostenol in patients with primary pulmonary hypertension

STUDY OBJECTIVE: To obtain information about the diagnosis and management of primary pulmonary hypertension (PPH), especially about the use of epoprostenol (Glaxo-Wellcome; Research Triangle Park, NC) in this patient population. BACKGROUND: Long-term IV epoprostenol therapy was approved recently for use in patients with PPH who are unresponsive to conventional therapy. Although epoprostenol represents a major advance in the treatment of PPH, there is no published consensus regarding the optimal use of this therapy. METHODS: A five-page survey was mailed to 23 investigators at medical centers treating five or more patients with PPH with long-term epoprostenol therapy. RESULTS: Nineteen of 23 investigators responded to the survey. During the initial hemodynamic evaluation, 11 investigators used changes in pulmonary vascular resistance (PVR), pulmonary artery pressure (PAP), and cardiac output, 5 investigators considered PVR and PAP only, and 2 investigators analyzed PVR alone to define a short-term vasodilator response. During long-term therapy, two thirds of the investigators increased the dose at scheduled intervals, while all investigators increased the dose in response to worsening symptoms. Epoprostenol doses were reported to range from 0.5 to 270 ng/kg/min. Nine investigators routinely repeated right heart catheterization an average of 7.5+/-3.8 months after starting epoprostenol, and the mean decrease in pulmonary artery pressure was between 15 and 25%. CONCLUSION: This survey indicates that there is wide variation in the evaluation of patients with PPH and in the use of epoprostenol therapy. The lack of consensus suggests the need for multicenter collaborative studies in order to optimize the use of epoprostenol therapy for PPH.     

A retrospective radiographic survey of embedded primary molar roots in Saudi adult patients

We compared the fluid-attenuated inversion recovery (FLAIR) sequence with conventional spin-echo (SE) imaging for detection of involvement of the central nervous system in five patients with myotonic dystrophy (MD). The diagnosis was made based on clinical features and DNA analysis. All patients showed abnormal high-intensity lesions in the white matter on T2-weighted images, although these were more clearly visible using FLAIR.     

反钙钛矿结构InNNi_3的电子结构、弹性性质和化学键结合的第一性原理研究

利用密度泛函理论(density funclional theory,DFT)的局域密度近似(localized density approximatin,LDA)和广义梯度近似(general gradient approximatin,GGA)研究反钙钛矿结构氮化物InNNi3晶体的电子结构、弹性性质和化学键结合特点。结果表明计算的晶格参数和平衡态体积与文献报道结果符合较好。能带结构的计算结果说明InNNi3具有金属性质,态密度和分态密度计算结果显示费米能级附近的态密度主要来自Ni-3d态的贡献。由VOIGT、REUSS和HILL’s(VRH)近似从计算得到的单晶弹性常数推导出多晶弹性模量,结果表明InNNi3为延性化合物。原子布居分析显示In、N原子间有较多的电荷转移,成键布居分析表明该氮化物为离子?共价混合键型化合物,即InNNi3是1种具有金属性的、共价一离子混合型的延性化合物。     

Properties and structure of niobium carbide heating elements

Conclusions In operation at 1900°C in a carbon-free atmosphere at a residual pressure of 10^–2-2· 10^–3 Pa a heating element of composition NbC + Nb₂C + Nb experiences a steady loss of carbon at a rate of 0.5–1 m/h from its surface, with the formation of a metallic phase. Heating elements of this composition may be recommended for service in vacuum resistance furnaces at temperatures of up to 1900°C, where they can be expected to have a useful life of the order of 1000 h. Niobium monocarbide heating elements operating at 2100–2500°C in a carbon-containing atmosphere under a pressure of 10^–2-2·10^–3 Pa experience no change in phase composition or shape and only minor changes in structure, and possess good thermal fatigue resistance. They can thus be employed in vacuum electric furnaces under these conditions. Long experience (more than two years) with the operation of a laboratory vacuum electric furnace with a niobium carbide heating element in the temperature range 1000–1500°C has demonstrated that the use of niobium carbide heating elements widens scope for new electro-thermal equipment.Translated from Poroshkovaya Metallurgiya, No. 3(231), pp. 92–97, March, 1982.     

Protein secondary structure prediction by the analysis of variation and conservation in multiple alignments

A number of methods exist for the prediction of protein secondary structure from primary sequence. One method identifies variable charged and conserved hydrophobic residues within large multiple alignments as a means of indicating outside and inside sites respectively in the protein structure. These sites are then manually fitted to secondary structure templates to generate a secondary structure prediction. Using the existing theoretical bases of this method, we present an algorithm (STAMA) which automatically carries out the initial variation/conservation analysis of the alignment. We also test the accuracy of complete predictions carried out by manual fitting of the STAMA-derived assignments to structure templates, using five large multiple alignments each including a protein of known structure. The method was found on average to predict only 57% of residues in the correct secondary structure, and was only as accurate as predictions carried out using the established and automated method of Garnier, Osguthorpe and Robson (1978) applied to a single sequence. When used in conjunction with other secondary structure prediction methods, however, the resulting consensus predictions were found to be very accurate, with 78% of the elements (alpha helices or beta strands) for which a consensus could be obtained being predicted correctly. The algorithm presented here, plus the assessment of the accuracy of prediction generated by this method, should enable this predictive approach to receive informed general use.     

Differential subsequence conservation of interspersed repetitive Streptococcus pneumoniae BOX elements in diverse bacteria

Evolutionary conservation of an interspersed repetitive DNA sequence, BOX, from Streptococcus pneumoniae was investigated to explore the mosaic nature of these elements. BOX elements consist of various combinations of three subunits, boxA, boxB, and boxC. Eight oligonucleotide probes were designed based on consensus DNA sequences of boxA, boxB, and boxC subunits. DNA hybridization studies and PCR using these probes/primers demonstrate that oligonucleotide sequences within the boxA subunit appear to be conserved among diverse bacterial species. The boxB and boxC subunits show only limited, if any, sequence conservation in bacteria other than S. pneumoniae. Intact BOX elements with boxA, boxB, and boxC subunits were only present in high copy number in pneumococcal strains. This pattern of differential conservation lends support to the modular nature of BOX repetitive elements in that boxA-like subsequences are effectively independent of boxB-like or boxC-like subunits in bacteria other than S. pneumoniae. Furthermore, dendrograms derived from repetitive sequence-based PCR (rep-PCR) fingerprints of S. pneumoniae isolates using the BOXA1R primer yielded clustering patterns that were similar to those obtained previously by other methods, suggesting that these repetitive sequence-based DNA fingerprints represent intrinsic properties of an S. pneumoniae strain's genome. Our results indicate widespread conservation of boxA-like subsequences in the bacterial kingdom, lend support to the mosaic nature of BOX in S. pneumoniae, and demonstrate the utility of boxA-based primers for rep-PCR fingerprinting of many microorganisms.     

Essential nucleotide sequences and secondary structure elements of the hairpin ribozyme

In vitro selection experiments have been used to isolate active variants of the 50 nt hairpin catalytic RNA motif following randomization of individual ribozyme domains and intensive mutagenesis of the ribozyme-substrate complex. Active and inactive variants were characterized by sequencing, analysis of RNA cleavage activity in cis and in trans, and by substrate binding studies. Results precisely define base-pairing requirements for ribozyme helices 3 and 4, and identify eight essential nucleotides (G8, A9, A10, G21, A22, A23, A24 and C25) within the catalytic core of the ribozyme. Activity and substrate binding assays show that point mutations at these eight sites eliminate cleavage activity but do not significantly decrease substrate binding, demonstrating that these bases contribute to catalytic function. The mutation U39C has been isolated from different selection experiments as a second-site suppressor of the down mutants G21U and A43G. Assays of the U39C mutation in the wild-type ribozyme and in a variety of mutant backgrounds show that this variant is a general up mutation. Results from selection experiments involving populations totaling more than 10(10) variants are summarized, and consensus sequences including 16 essential nucleotides and a secondary structure model of four short helices, encompassing 18 bp for the ribozyme-substrate complex are derived.     

Significance of presence of teratomatous elements in the primary tumour of testicular cancer

Foveal discrimination thresholds were measured for orientation, vernier alignment, bisection, displacement detection and stereoscopic acuity using simple line stimuli and also sinusoidal grating patches with gaussian intensity modulation (Gabor stimuli). Stimulus parameters such as luminance, exposure duration, component separation and, as far as possible, length were identical for both. Orientation discrimination as a function of length is almost identical for the two classes of stimuli, some observers performing slightly better with Gabor patches. Thresholds for displacement detection are also the same. Vernier, stereo and bisection acuities, however, are considerable better with line than with Gabor stimuli.