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An absolute method for the determination of the persistence length of native DNA from electron micrographs
Author(s) -
Frontali C.,
Dore E.,
Ferrauto A.,
Gratton E.,
Bettini A.,
Pozzan M. R.,
Valdevit E.
Publication year - 1979
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1979.360180604
Subject(s) - persistence length , tangent , gaussian , chemistry , curvature , orientation (vector space) , biological system , statistical physics , optics , molecular physics , molecule , physics , mathematics , computational chemistry , geometry , organic chemistry , biology
Information on spatial correlation in the tangent direction along electron microscope images of filamentous molecule is shown to be obtainable by the analysis of statistical fluctuations in curvature, yielding an absolute measure of the persistence parameter a micro . The relationship of a micro , a local, microscopic parameter, to the persistence length introduced by Kratky and Porod is discussed. The hypotheses underlying the assumed theoretical model concern (1) the shape of the angle distribution, assumed to be Gaussian; (2) the passage from a three‐ to a two‐dimensional situation, which is supposed to occur by deformation of the flexible chain in a manner that preserves the memory of the spatial correlation in orientation (except for the blocking of one degree of freedom); and (3) the adsorption conditions, which should meet the equilibrium requirement as closely as possible. The analytical method has been checked on computer simulated “Gaussian” molecules: the study of the simulated sample was essential in solving the problems connected with minimum statistics requirements and the effect of the reading error. Experimental images obtained for T2 DNA fragments at different ionic strengths by Kleinschmidt's adsorption technique have been analyzed by means of an automatic flying spot digitizer, the “Precision Encoder and Pattern Recognition.” The results show that adsorbed molecules do in fact “remember” the rigidity they possessed in solution and that the Gaussian hypothesis is well verified. Consequently, the slopes of log cosθ ( l ) or θ 2 ( l ) may be used indifferently in the estimate of a micro . The dependence of this parameter on ionic strength in the range explored shows the expected behavior.