Characterization of rodlike DNA fragments

✍ Scribed by M. Record Thomas Jr.; Charles P. Woodbury; Ross B. Inman

• Publisher: Wiley (John Wiley & Sons)
• Year: 1975
• Tongue: English
• Weight: 901 KB
• Volume: 14
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1975.360140212

✦ Synopsis

Native calf thymus DNA was sheared by sonication in a viscous solvent to the molecular-weight range from 3 x lo4 to 3 x lo5 daltons, and fractionated by gel chromatography. Number and weight average molecular weights (a, and aw) were determined for individual fractions by electron microscopy; the ratio a,,,/~@,, for the peak fraction is approximately 1.1. Sedimentation coefficients (so~o.,) of these fractionated samples show an approximately linear dependence on the logarithm of the molecular weight a,.

This behavior is that expected for rodlike molecules, and is in quantitative agreement with the theory ol Yamakawa and Fujii [(1973) Macromolecules 6, 407-4!5] for the sedimentajion coefficient of a wormlike chain with a per$stence length of 625 A, a diameter of 25 A, and a mass per unit length of 195 daltons/A. It appears that the wormlike coil model, without excluded volume, can represent the sedimentation behavior of DNA over the entire conformational range from rigid rod to flexible coil, using the above parameters.

Equilibrium melting curves were determined for various fractions in aqueous 2.4 M tetraethylammonium bromide. A substantial broadening of the transition and decrease of the melting temperature were observed with decreasing molecular weight. Empirical expressions have been obtained relating both the transition temperature and breadth in this solvent to molecular weight.