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91.
We present a base-pairing model of oligonucleotide duplex formation and show in detail its equivalence to the nearest-neighbor dimer methods from fits to free energy of duplex formation data for short DNA-DNA and DNA-RNA hybrids containing only Watson-Crick pairs. For completeness, the corresponding RNA-RNA parameters are included. In this approach, the connection between rank-deficient polymer and rank-determinant oligonucleotide parameter sets for DNA duplexes is transparent. The method is generalized to include RNA-DNA hybrids where the rank-deficient model with 11 dimer parameters in fact provides slightly improved predictions relative to the standard method with 16 independent dimer parameters (DeltaG mean errors of 4.5 and 5.4%, respectively). 相似文献
92.
93.
Beuning PJ Nagan MC Cramer CJ Musier-Forsyth K Gelpí JL Bashford D 《RNA (New York, N.Y.)》2002,8(5):659-670
Specific aminoacylation by aminoacyl-tRNA synthetases requires accurate recognition of cognate tRNA substrates. In the case of alanyl-tRNA synthetase (AlaRS), RNA duplexes that mimic the acceptor stem of the tRNA are efficient substrates for aminoacylation in vitro. It was previously shown that recognition by AlaRS is severely affected by a simple base pair transversion of the G2:C71 pair at the second position in the RNA helix. In this study, we determined the aminoacylation efficiencies of 50 variants of the tRNA(Ala) acceptor stem containing substitutions at the 2:71 position. We find that there is not a single functional group of the wild-type G2:C71 base pair that is critical for positive recognition. Rather, we observed that base-pair orientation plays an important role in recognition. In particular, pyrimidine2:purine71 combinations generally resulted in decreased aminoacylation efficiency compared to the corresponding purine:pyrimidine pair. Moreover, the activity of a pyrimidine:purine variant could be partially restored by the presence of a major groove amino group at position 71. In an attempt to understand this result further, dielectric continuum electrostatic calculations were carried out, in some cases with additional inclusion of van der Waals interaction energies, to determine interaction potentials of the wild-type duplexAla and seven 2:71 variants. This analysis revealed a positive correlation between major groove negative electrostatic potential in the vicinity of the 3:70 base pair and measured aminoacylation efficiency. 相似文献
94.
K Kertesz-Chaloupková PJ Walser JD Granado M Aebi U Kües 《Fungal genetics and biology : FG & B》1998,23(1):95-109
Monokaryotic mycelia of the homobasidiomycete Coprinus cinereus form asexual spores (oidia) constitutively in abundant numbers. Mycelia with mutations in both mating type loci (Amut Bmut homokaryons) also produce copious oidia but only when exposed to blue light. We used such an Amut Bmut homokaryon to define environmental and inherent factors that influence the light-induced oidiation process. We show that the Amut function causes repression of oidiation in the dark and that light overrides this effect. Similarly, compatible genes from different haplotypes of the A mating type locus repress sporulation in the dark and not in the light. Compatible products of the B mating type locus reduce the outcome of light on A-mediated repression but the mutated B function present in the Amut Bmut homokaryons is not effective. In dikaryons, the coordinated regulation of asexual sporulation by compatible A and B mating type genes results in moderate oidia production in light. Copyright 1998 Academic Press. 相似文献
95.
A radiographic technique for processing a large number of human crania was developed to aid in the diagnosis of porotic hyperostosis in a large skeletal population. These images are made directly onto photographic paper, thereby reducing costs and increasing the rate of processing. The technique is especially well suited for radiographing human skeletal material and gives excellent diagnostic image quality. 相似文献
96.
The interaction of pore-forming agents, such as Sendai virus, influenza virus (at pH 5 3), activated complement,Staphylococcus aureus α-toxin, melittin and polylysine, with the surface membrane of cells has been studied. In each case the following changes are
initiated: collapse of membrane potential, leakage of ions, and leakage of phosphorylated metabolites. The changes can be
inihibited by extracellular Ca2+ at physiological concentration; Mg2+ is less effective, and Zn2+ is more effective, than Ca2+ Ca2+ appears to act at a stage subsequent to the binding of pore-forming agent to cells. It is concluded that divalent cations
are able to protect cells against the damaging effects of certain viruses, toxins or the components of activated complement
in a manner that is worthy of further investigation. 相似文献
97.
Production and characterization of a monoclonal antibody able to discriminate galectin-1 from galectin-2 and galectin-3 总被引:1,自引:0,他引:1
Cornillot JD; Pontet M; Dupuy C; Chadli A; Caron M; Joubert-Caron R; Bourin P; Bladier D 《Glycobiology》1998,8(5):425-432
Antisera raised against galectin-1 exhibit crossreactivities with other
galectins or related molecules. In order to overcome this problem, a
monoclonal antibody to human brain galectin-1 was obtained by selecting
clones without reactivity toward galectin-3. This mAb specifically bound
galectin-1 of various animal origins but neither galectin-2 nor galectin-3.
Western-blotting analysis of soluble human brain extracts after 2D gel
electrophoresis revealed only the two most acidic isoforms of galectin-1.
The ability of this mAb to bind galectin-1/asialofetuin complexes indicates
that its epitope is not localized in the carbohydrate recognition domain of
galectin-1. This particularity induces with efficiency its monospecificity.
相似文献
98.
C. Lindsay Bashford 《Bioscience reports》1995,15(6):553-565
Flow of ions through narrow pores, either induced in biological membranes or created in synthetic membrane filters, exhibits, under appropriate conditions: 1) rapid switching of ion current between high and low conducting states; 2) selectivity between different ions; 3) inhibition by protons or divalent cations with an order of efficacy usually H+ >Zn2+>Ca2+ >Mg2+. It seems reasonable to conclude that these common properties arise from a common cause-the nature of the flow of ions close to a charged surface. 相似文献
99.
Y. E. Korchev C. L. Bashford G. M. Alder J. J. Kasianowicz C. A. Pasternak 《The Journal of membrane biology》1995,147(3):233-239
We have used a polymer-exclusion method to estimate the sizes of the high and low-conductance states of Staphylococcus aureus -toxin channels across planar lipid bilayers. Despite a >10-fold difference in conductance between high and low-conductance states, the size differs by <2-fold. We conclude that factors other than the dimensions have a strong influence on the conductance of -toxin channels. We also show that the high conductance state is destabilized by the presence of high molecular weight polymers outside the channel, compatible with the removal of channel water as the high conductance state shrinks to the low conductance state.We are grateful to Drs. D.T. Edmonds, A.A. Lev and V.A. Parsegian for fruitful discussion and to the Cell Surface Research Fund, the Science and Engineering Research Council, The Wellcome Trust, UNESCO (Molecular and Cellular Biology Network) and the National Academy of Sciences/National Research Council for financial support. 相似文献
100.
An anchored restriction-mapping approach applied to the genetic analysis of the Anopheles gambiae malaria vector complex 1 总被引:1,自引:0,他引:1
We introduce here a simple approach for rapidly determining restriction
maps for a number of regions of a genome; this involves "anchoring" a map
with a rare restriction site (in this case the seldom-cutting EagI)
followed by partial digestion of a frequent-cutting enzyme (e.g., Sau 3A).
We applied this technology to five species of the Anopheles gambiae
complex. In a single Southern blot we obtained about a 15-kb restriction
map each for the mtDNA, rRNA gene, and a scnDNA region for each of five
species. Phylogenetic analyses of these regions yield trees at odds with
the more traditional chromosome inversion-based trees. The value of the
approach for systematic purposes is the ease with which several large,
independent regions of the genome can be quickly assayed for molecular
variation.
相似文献