ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Dynamic light-scattering techniques are employed to study the internal Brownian motions of a commercial calf thymus DNA, clean and contaminated φ29 DNAs, and a clean φ29 DNA with bound spermidine as a function of pH. The Rouse-Zimm model parameters of both calf thymus and contaminated φ29 DNAs differ substantially from those of clean φ29 DNA in the neutral-pH region. However, this difference is largely removed by adding 0.01M EDTA (which has no effect on clean φ29 DNA) to the calf thymus DNA sample. These findings imply the existence in that preparation of polycation contaminants, presumably basic proteins, that can substantially alter the local mechanical properties of the DNA near their binding sites. The internal motion parameters kBT/f and b of both calf thymus and contaminated φ29 DNAs are found to exhibit pronounced characteristic variations between pH 8.5 and 10.5, over which range there is essentially no detectable titration to a resolution of about 1% of the base pairs. These variations, which are not observed for clean φ29 DNA, are qualitatively similar to those previously reported for a φ29 DNA with 21 single-strand breaks per chain. This indicates the formation of titratable joints associated with bound polycation contaminants. These basic ligands presumably facilitate local denaturation by stabilizing the titration of one or more protons on base-ring nitrogens near their binding sites. Spermidine binding up to 85-87% of neutralization of the total DNA charge has only a relatively minor effect on the internal motion parameters at neutral pH in 0.01M NaCl. However on raising the pH to 10.2, the internal motion parameter kBT/f undergoes a marked decrease similar to that observed for both calf thymus and contaminated φ29 DNAs and also φ29 DNA with single-strand breaks. This indicates that spermidine, too, is capable of inducing titratable joints. Evidence is presented that the titratable joints associated with bound polycations on the calf thymus DNA may serve primarily as torsion joints, as was found previously for the titratable joints associated with single-strand breaks.
Additional Material:
11 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.1981.360200115
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