摘要:

AbstractWe have synthesized and studied the CD spectra of five new double‐stranded RNA polymers: poly[r(A‐G)·r(C‐U)], poly[r(A‐U‐C)·r(G‐A‐U)], poly[r(A‐C‐U)·r(A‐G‐U)], poly[r(A‐A‐C)·r(G‐U‐U)], and poly[r(A‐C‐C)·r(G‐G‐U)]. Together with previously published spectra of seven other RNA sequences, the spectra of these new sequences provide a library sufficient to approximate the spectra of all other RNA sequences by first‐neighbor formulas and, in addition, give four spectra with which we may test the validity of first‐neighbor approximations. (1) We find that the spectra of RNA sequence isomers are very different, but that the spectra essentially do obey first‐neighbor relationships. (2) We have derived tentative first‐neighbor assignments of negative bands at about 295 and 210 nm in the CD spectra. (3) A test of spectral independence shows that among the 12 polymer spectra there are at least seven significant independent spectral shapes, one less than the eight needed to give the most accurate spectral analysis of an unknown RNA sequence for its first‐neighbor frequencies. (4) Spectra are calculated for RNAs of random base composition, approximating natural RNAs having complex sequences. (5) AT‐matrix of spectral components assigned to the first‐neighbor base pairs is derived from 10 of the spectra. This matrix allows an estimation of the CD spectrum of any other known RNA sequence or an analysis of the spectrum of an unknown sequence for its distribution of first‐neighbor base‐pair frequencies. (6) Test analyses of two of the synthetic polymers and of two natural RNAs set a probable limit on the accuracy of first‐neighbor frequency determinations using thisT‐matrix. (7) Finally, we summarize in an appendix the melting temperatures for all the RNA and corresponding DNA sequences; it appears that theTmvalues of bo

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200702

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractThe proton nmr spectra of the oligoribonucleotides in the series CpXpG, ApXpG, CpApXpUpG, and ApGpXpC (X= A, G, C, and U), together with the reference compounds CpG, ApG, CpApUpG, and ApGpC, have been measured. A complete analysis of all the nonexchangeable base protons and the ribose H‐1′ protons was made. The insertion of a nucleotideXinto a oligoribonucleotide led to shift changes at both nearest‐neighbor and next‐nearest‐neighbor positions, which were rationalized in terms of the shielding abilities of the various bases. The derived shielding trends in the ApGpXpC series of compounds were successfully used to predict the chemical shifts of resonances in the related ApGpXpC

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200703

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractHeavy meromyosin binding to F‐actin saturated with tropomyosin is studied theoretically. The problem is formulated as a special case ofn‐mer adsorption to a one‐dimensional Ising lattice which is divided intom‐site‐lo

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200704

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractChitosan flakes from shrimp shells and xerogels derived from branched 1‐deoxyglycit‐1‐yl chitosan derivatives were examined by scanning electron microscopy; the former displayed relatively large, dome‐shaped orifices and the latter were found to exhibit a wide variety of ultrastructures, ranging from smooth, nonporous to microporous and microfibrillar. Some correlation between the chemical structure of the side chains of the chitosan derivatives and their microarchitecture could be esta

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200705

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractConformational properties have been examined for three proteins which are disordered when dissolved in water but become partially ordered in the presence of anionic lipids. The three proteins, which play important roles in the central nervous system, are myelin basic protein, β‐endorphin, and β‐lipotropin. When evaluated using matrix methods, the helical content of each protein is predicted to be vanishingly small in water, in agreement with experiment. Unperturbed root‐mean‐square radii of gyration are also evaluated for these proteins in water using generator matrices, which have seen wide application to synthetic polymers. Agreement between computed and measured dimensions is found to be excellent. Having successfully described the conformations of myelin basic protein, β‐endorphin, and β‐lipotropin in water, attention is then directed to the changes induced upon interaction with anionic lipids or detergents. Computations predict an increase in helical content, with numerical results being in quite good agreement with experimental observations using several anionic lipids. Examination of the helix‐propagation‐probability profiles reveals an interesting feature of regions where this probability is high. When folded into a α‐helix, these regions show one surface where the only side chains are hydrophobic. Charged side chains (with positive charges predominating) are found on the other surface of the helical segment. The arrangement of side chains on these helices is thus well suited to promote favorable interactions with a membrane containing anionic lipids. Examples of the occurrence of these helices are provided by amino acid residues 13–25 and 130–157 in myelin basic protein and res

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200706

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractThe host–guest technique has been applied to the determination of the helix–coil stability constants of two naturally occurring amino acids,L‐alanine andL‐leucine, in a nonaqueous solvent system. Random copolymers containingL‐alanine andL‐leucine, respectively, as guest residues and γ‐benzyl‐L‐glutamate as the host residue were synthesized. The polymers were fractionated and characterized for their amino acid content, molecular weight, and helix–coil transition behavior in a dichloroacetic acid (DCA)–1,2‐dichloroethane (DCE) mixture. Two types of helix–coil transitions were carried out on the copolymers: solvent‐induced transitions in DCA–DCE mixtures at 25°C and thermally induced transitions in a 82:18 (wt %) DCA–DCE mixture. The thermally induced transitions were analyzed by statistical mechanical methods to determine the Zimm‐Bragg parameters, σ ands, of the guest residues. The experimental data indicate that, in the nonaqueous solvent, theL‐alanine residue stabilizes the α‐helical conformation more than theL‐leucine residue does. This is in contrast to their behavior in aqueous solution, where the reverse is true. The implications of this finding for the analysis of helical st

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200707

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractThe thermal‐denaturation transition of ribonuclease S (RNAase S) is measured by circular dichroism at 225 nm. Only conformational transitions involving the S‐peptide–S‐protein complex are detected at this wavelength. Different pathways of thermal unfolding at high and low concentrations are apparent: at low concentrations the temperature of half‐completion of denaturation (Tm) varies with concentration. Above a total enzyme concentration of 50 μM,Tmremains constant. The observed data can be explained on the basis of a model where the association–dissociation step occurs between S‐peptide and thermally (at least partly) unfolded S‐protein. The complex as a whole undergoes a major folding–unfolding transition in the course of which the S‐peptide μ‐helix appears to be formed. The unfolded complex is well populated in the unfolding transition region for enzyme concentrations of 100 μMor more. The model succeeds in deducing thermodynamic parameters from the thermal denaturation curves in various different ways. The values thus obtained are fully self‐consistent and, moreover, consistent with the values for the apparent association constant and apparent association enthalpy as measured in enzyme‐dilution experime

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200708

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractA Monte Carlo analysis is presented which establishes a relationship between the rotational diffusion coefficients and the flexibility (persistence length,P) of short, wormlike chains. The results of this analysis are presented in terms of experimentally observable quantities; namely, the rotational relaxation times for the field‐free decay of optical anisotropy. The pertinent theoretical quantity isR, defined as the ratio of the longest rotational relaxation time of a wormlike chain to the transverse rotational relaxation time of a rigid cylinder having the same axial length (L) and segmental volume.R, so defined, is essentially independent of the axial ratio of the cylinder for any value ofL/Pwithin the range of validity of the present analysis (axial ratio>20; 0.1

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200709

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractIn the preceding article, a Monte Carlo analysis was presented which provides a quantitative numerical relationship between the rotational diffusion coefficients, as measured by the decay of optical anisotropy following an electric field pulse, and the flexibility (persistence length) of short, wormlike chains. In the present article, the results of the foregoing analysis are applied to the observed rates of decay of birefringence for a series of sequenced DNA fragments ranging in size from 104 to 910 base pairs. Under the conditions used in this study, the DNA fragments exist as native, duplex molecules. Furthermore, conditions are defined in which the observed relaxation times are not dependent on DNA concentration, field strength, or the duration of the pulse. It is pointed out that the ionic atmosphere associated with a wormlike polyion does not exert any significant (direct) influence on the rotational diffusion of the polyion and, therefore, that the rotational relaxation times are a true measure of the configurations of the DNA molecules in solution. Moreover, excluded‐volume effects are shown not to be significant for the moderately short molecules employed in this study. The major conclusion of this study is that there is no strong ionic strength dependence of the persistence length for ionic strengths above 1 mMand that the persistence length, under conditions where electrostatic contributions are negligible, is approximately 500 Å. For ionic strengths significantly lower than 1 mM, electrostatic contributions to the stiffness of DNA become significa

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200710

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractSolvents which accelerate DNA renaturation rates have been investigated. Addition of NaCl or LiCl to DNA in 2.4MEt4NCl initially increases renaturation rates at 45°C and then leads to a loss of second‐order behavior. The greatest accelerations are seen with LiCl and dilute DNA. Volume exclusion by dextran sulfate is the most effective method of accelerating DNA renaturation with concentrated DNA. Addition of dextran sulfate beyond 10–12% in 2.4MEt4NCl fails to increase the acceleration beyond approximately 10‐fold. Accelerations of 100‐fold may be achieved with 35–40% dextran sulfate in 1MNaCl at 70°C. No other mixed solvent system was found to be more effective, although acceleration may be achieved in solvents containing formamide or other denaturants. The acceleration in 2MNaCl occurs without loss of the normal concentration and temperature dependence of DNA renaturation and is also independent of dextran sulfate concentration if sufficient dextran sulfate is used. Dextran sulfate may be selectively precipitated by us

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200711

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY