Kimiko Matsuo

Interaction of poly-l-lysine and nucleic acids

Interactions of poly- L -lysine with poly (I + C) and with thymus DNA in dilute solutions and in low ionic strength have been studied. The helix-coil transition of the polynucleotides in the reaction was followed by optical density at 248 mμ, or 260 mμ Both of these poly- L -lysine plus polynucleotide solutions gave a two-step transition, one of which (at a lower temperature) corresponds to the melting of the free polynucleotide double helix and the other (at a higher temperature) corresponds to the melting of a poly- L -lysine-polynucleotide complex. These transition temperatures are independent of the poly- L -lysine concentration added. However, as the poly- L -lysine concentration increases in the mixture, the hyperchromicity at the first transition decreases proportionately, together with a corresponding increase of hyperchromicity at the second transition. The poly- L -lysine-polynucleotide complex and the free polynucleotide were resolved by means of sucrose density-gradient electrophoresis. The behavior of the DNA molecules in the binding reaction can be monitored by the help of 32P-labeled DNA in the electrophoresis experiments. These results show that at room temperature and in a dilute salt solution, the poly- L -lysine-polynucleotide binding reaction is quantitative, irreversible and with a definite stoichiometric ratio. The lysine/nucleotide ratio in the poly- L -lysine-DNA complex was determined to be 1 : 1 and in the poly- L -lysine-poly (I + C) complex to be 0-5 : 1.

Interaction of poly-l-lysine with nucleic acids: IV. A sedimentation and electron-microscopic study

Abstract A mixture of poly- l -lysine plus calf thymus DNA (lysine/nucleotide mole ratio = 0.5 in solution was subjected to low-speed centrifugation. It was found that the complex molecules, each of which was previously shown to have a triple-helical structure of two polynucleotide and one polypeptide chain, form a larger aggregate in solution, and that such an aggregate is soluble under ordinary gravitational forces but not in a gravitational field of 5000×g. The shape of such an aggregate was examined electron-microscopically. The aggregates of rice dwarf virus RNA plus poly- l -lysine prepared in a 0.5 M salt solution were observed as vermiform clumps of almost equal size; their diameters were mostly about 500 A and their lengths 2000–3000 A. The size of the aggregate of DNA plus poly-L-lysine, on the other hand, was found to be much more variable.