FLEXIBILITY OF LOW-MOLECULAR WEIGHT DOUBLE-STRANDED DNA AS FUNCTION OF LENGTH .1. ISOLATION AND PHYSICAL CHARACTERIZATION OF 7 FRACTIONS

Sonicated calf thymus DNA was fractionated by rate zonal centrifugation into 7 fractions with weight average MW ranging from 0.28-1.3 .times. 106 daltons, as determined by sedimentation equilibrium and light scattering measurements. EM and sedimentation equilibrium analysis revealed these fractions to be narrowly disperse with Mw/Mn [weight average molecular weight/number average molecular weight] ratios averaging about 1.06. Intrinsic viscosities and sedimentation rates were measured and found to vary linearly with molecular weight in double-logarithmic plots in fair agreement with previously published functions relating these parameters for low molecular weight DNA. The average value for .beta. from the Mandelkern-Flory equation was 2.59 .times. 106, also agreeing with reported estimates of this parameter for short DNA. These data are used in the 2nd paper of this series to calculate the persistence length of the DNA fragments in each of the 7 fractions by light scattering and hydrodynamic theories for the Kratky-Porod worm-like coil.