DEOXYRIBONUCLEIC ACID-POLYLYSINE COMPLEXES . STRUCTURE AND NUCLEOTIDE SPECIFICITY

The reversible interaction of polylysine with deoxyribonucleic acid has been examined. It is found that under appropriate conditions the reaction is stoichiometric (one lysine residue per nucleotide), cooperative, and with deoxyribonucleic acid samples heterogeneous in base composition, almost completely selective for the A.T-rich fraction. Although preference for A.T-rich deoxyribonucleic acid persists under a variety of conditions, it can be reversed in the presence of tetramethylammonium ion, resulting in selective interaction of polylysine with G.C-rich deoxyribonucleic acid. Under conditions of reversible and selective complex formation, the polylysine-deoxyribonucleic acid complex exists in a separate aggregated phase. The properties of this phase have been studied by sedimentation velocity and light-scattering methods. The particles containing the complex are highly solvated and remarkably uniform in size with an average radius of about 1700 Å, varying little with the size of deoxyribonucleic acid used in the molecular weight range 107-1.2 X 108. The optical rotatory properties of the complex are unusual. Under optimal conditions, the observed residue rotations in the region 250-290 nm are between 50 and 100 times as large as those observed for deoxyribonucleic acid alone, and the observed circular dichroism and optical rotatory dispersion curves are quite different from those of deoxyribonucleic acid. Similar results are obtained whether poly-D-lysine or poly-L-lysine is used in forming the complex. It appears likely that these changes arise either from a perturbation of the deoxyribonucleic acid secondary structure which accompanies complex formation, or from the formation within the particle of a structure with long-range order. © 1969, American Chemical Society. All rights reserved.