Different effects of polylysine and polyarginine on the transition to a condensed state of DNA in solution

Circular dichroism spectroscopy has been used to investigate the influence of polylysine and polyarginine on the transition to a condensed state of DNA brought about by high concentrations of polyethyleneglycol and salt. From the dependence on DNA concentration of the CD signals, the anomalous CD of free DNA in polyethyleneglycol salt solution was attributed to the intermolecular association of DNA molecules. The CD spectral changes in polyethyleneglycol salt solution of the DNA · polylysine complex were indistinguishable from those of free DNA while the DNA · polyarginine complex suffered much smaller spectral changes as compared with free DNA, at low DNA concentrations where time-independent CD spectra were observed in polyethyleneglycol salt solution for both the complexed and free DNA. The repression of the spectral change by the latter complex was more remarkable at higher ratios of polyarginine to DNA. The facts indicate that, whereas polylysine binding has little influence on the intermolecular structural transition of double-stranded DNA into a compact molecular configuration in polyethyleneglycol salt solution, polyarginine binding has an effect of inhibiting the transition.