No abstract

Interaction between cetyltrimethylammonium bromide (CTAB) and large T4DNA was studied by potentiometric titration using an ion-selective membrane electrode. The data obtained were assessed in terms of recently reported results regarding the higher order structure of T4DNA with the addition of CTAB: individual DNA chains exhibit discrete phase-transition between random coil and compact globule states. The apparent cooperativity represented as a sigmoidal function is attributed to bimodality in the distribution between the elongated coil and compact globule states of T4DNA chains. In addition, the globule-coil transition of single T4DNA is reversible, demonstrated by single-molecule observation with fluorescence microscopy. At a fixed concentration of CTAB, transition from the globule to the coil state is brought about by the addition of polyacrylic acid, suggesting that this reversible transition may be used for the purification of giant DNA molecules.

No abstract

Investigations have been carried out to clarify the binding interactions between two kinds of native DNA:  one from salmon sperm (300−500 bp) and another from bacteriophage T4dC (166 kbp) and amine-terminated, diaminobutane core, poly(propylene imine) dendrimers (Astramol) of five generations (G1, G2, G3, G4, and G5). All dendrimers interacting with DNA at an equal concentration of amine and phosphate groups form electroneutral water-insoluble interpolyelectrolyte complexes (IPECs). However, G4 and G5 added to DNA solution in excess form positively charged water-soluble IPECs representing perfect objects to investigate the state of DNA molecules incorporated into IPEC. Using UV spectroscopy and CD spectroscopy combined with ultracentrifugation, it is shown that complexed DNA compacts, revealing a wound double-helical structure. Using fluorescence microscopy, we observed compaction of individual ultrahigh molecular mass DNA interacting with excess of G4 to form water-soluble positively charged IPECs “unimers”.