CHANGES IN MOLECULAR-WEIGHTS AND MOLECULAR-WEIGHT DISTRIBUTIONS OF DIFFERENTLY STRANDED NUCLEIC-ACIDS AFTER SONICATION - GEL-PERMEATION CHROMATOGRAPHY LOW-ANGLE LASER-LIGHT SCATTERING EVALUATION AND COMPUTER-SIMULATION

Changes of weight-average molecular weights (M(w)) and the molecular w eight distributions in terms of weight fraction (g(w)) were evaluated in the course of sonication for three nucleic acids in different confo rmations by the gel permeation chromatography/low angle laser light sc attering (GPC/LALLS) method. High M(w) samples used were single-strand ed poly(uridylic acid), (U)(n), double-stranded DNA, and triple-strand ed poly(adenylic acid). 2poly(inosinic acid), (A)(n) . 2(I)(n), in 0.2 -0.1 M NaCl at 0 degrees C. The experimental g(w) vs M curves were com puter-simulated for different chain-scission mechanisms: (1) random, ( 2) midpoint, (3) Gaussian, (4) classical partially random, and (5) new ly proposed partially random scission models. In comparison with the G PC/LALLS data, the middle portion of each single- or multiple-stranded chain was sheared randomly, whereas the adjacent end portions of the chain resisted sonic scission. The M(w) value of each intact end porti on was 1.0 x 10(5) for (U)(n), 1.5 x 10(5) for DNA, and 1.7 x 10(5) fo r (A)(n) . 2(I)(n), corresponding to the lowest possible M(w) for the sonicated but unfractionated nucleic acid samples under the present co nditions.