摘要:

AbstractUsing the interaction of polyacrylic anhydride with uridine orN‐acetyl derivatives of adenosine, cytidine, and guanosine, the water‐soluble copolymers, polyacryloylnucleosides, were obtained. The acryloylnucleoside units to acrylic acid units ratio in the copolymer was usually about 1:20. The attaching of nucleosides to the polymer occurs mostly through the 5′‐hydroxyl group of the sugar.The prominent feature of all polyacryloylnucleosides obtained is their fibrous structure at an ionic strength 0.2 and neutral pH. At concentrations<200 μg/ml the separate strands with a length of 0.2–1.0 μ and diameter of 30–40 Å are distinguishable. Evidently they are formed by side association of two molecules of copolymer or by folding of one molecule on itself. At higher concentrations branched multistranded structures are formed. In the same conditions polyacrylic acid alone does not form the fibrous structures.Heating of polyacryloylnucleoside solutions at 100°C and fast cooling in ice water, or raising of the pH to 12 turned the stranded structures to coils. After annealing or neutralization the stranded structures reformed. These transformations are similar to those which occur with nucleic acids. The results show that the fibrous structure of the copolymers depends on the hydrogen bonds formed by purine and/or p

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130112

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

年代:1974

数据来源: WILEY

摘要:

AbstractSystematic experimental data for the dependence of melting range width ΔTfor phage T2 and calf thymus DNA's on sodium ion concentration was obtained. A mathematical description of helix‐coil transition was given for the case of DNA with a block sequence of nucleotides (such as calf thymus DNA). This description predicts an almost linear dependence of ΔTfor DNA from higher organisms on the valueTGC‐TAT. On the other hand, ΔTis proportional to (TGC‐TAT)1.6for DNA's with quasi‐random sequences (such as phage T2 DNA). Experimental data fully confirmed the theoretical predictions.The dependence ofTGC‐TATon sodium ion concentration was determined. The most striking feature of this dependence is the sharp rise inTGC‐TATin the region of low sodium ion concentration (<3 × 10−3) up to 100°C. The dependence ofTGCand ofTATon ionic strength was calculated separately. In the region of low ionic strength, these quantities show markedly

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130113

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe viscosity of the DNA of T2 bacteriophage has been studied with the aim of understanding the folding of the DNA in the phage head. Thus the results of previous workers have been extended into a range of concentrations and mixtures of cations and polyamines simulating the conditions obtaining in actual phage heads. Difficulties in obtaining reproducible results with DNA in 0.001MNaCl have been attributed to the presence of traces of protein, perhaps nulease(s), that can be eliminated by hot‐phenol extraction of the DNA. The results have been negative in the sense that the minimum viscosity obtained (120–140 dl/g) indicates a molecule that is far from tightly folded and in that viscosities in this range can be obtained with a simple mixture of Na+and Mg++. No specificity of the diamines putrescine and spermidine is seen; they are simply surrogate cati

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130114

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

年代:1974

数据来源: WILEY

摘要:

AbstractA model for the flexibility of DNA is proposed that is based on discrete variations in the direction of propagation in going from one subunit to the next. Expansion of the local free energy in terms of the local bending gives a Gaussian distribution function. The assumption of the independence of local bends on neighbors lead to very simple formulae for the persistence length and the characteristic ratio. Emphasis, however, is placed on the application of the formulae for molecules of finite size where the persistence length andC∞are not defined. The formulae are worked out for two models, which should serve as limits for the real physical situatio

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130115

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe heats of the conformational conversion ΔHcof polyuridylic acid (polyU) in the presence of various cations were determined using a differential scanning microcalorimeter and an isothermal mixing calorimeter. The first method yields a value of ΔHc= 5.2 kcal/mol of base pairs, the second one a value of ΔHc= 6.4 kcal/mol of base pairs. Knowing ΔHcand the maximal slope of the degree of conversion, which was determined from the temperature dependence of the absorbance of polyU solutions at 260 nm, we were able to evaluate the parameter of cooperativity σ. From the relation σ =e ΔF stack/RTthe stacking free energy ΔFstackcould be calculated. Dividing the apparent enthalpy of conversion by the calorimetrically measured enthalpy yields the cooperative lengthN0of one helical segment at the midpoint of conversion. The results show that the type of the cation has no influence on the magnitude of ΔHc, whereas the cooperativity of polyU is influenced by the var

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130116

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

年代:1974

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130117

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

年代:1974

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130101

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

年代:1974

数据来源: WILEY