Model nucleoprotein complexes: studies on the interaction of cationic homopolypeptides with DNA.

摘要: Abstract Complexes of natiye calf thymus DNA with the cationic polypeptides poly-lornithine, poly-l-lysine, poly-l-arginine and poly-l-homoarginine, have been prepared their solubility, stoichiometry, absorption spectra thermal denaturation studied. Increasing peptide cation/DNA phosphate ratio, up to electrostatic equivalence, yielded progressively more insoluble products increased turbidity “soluble” fraction. Certain spectral changes were observed which may be largely attributed anomalous scattering in absorbing region. Addition resulted a marked stabilization helix against denaturation. At ratios less than monitored at 260 280 mμ revealed biphasic transition profile: first had melting temperature similar under same solvent conditions; second was characteristic for type polypeptide complex. Thermal 350 (i.e., transitions) showed monophasic profile higher DNA-polypeptide The different stabilized extents. In order decreasing degree they are: poly-l-ornithine > poly-l-lysine poly-l-homoarginine. Analysis dispersion hyperchromicity demonstrated that preferentially stabilize A-T rich regions, whereas poly-l-homoarginine appear discriminating. soluble complexes could subfractionated by ultracentrifugation into fraction melted like “naked” DNA, complex ratio close equivalence. experimental data imply that, proper conditions annealing, basic form definable molecular structures DNA; binding reaction is stoichiometric co-operative. Model-building suggests interact either large or small groove DNA.