Stabilization of Z-DNA by polyarginine near physiological ionic strength

The identification of left handed or Z-DNA in solutions of poly d(GC) in high salt suggests that left handed DNA may exist in biological systems if stabilized at lower ionic strength. In the present study we show that binding of polyarginine to the Z form of poly d(GC) results in a protein-Z-DNA complex stable near physiological ionic strength. The percentage of Z-DNA in the low salt polyarginine-poly d(GC) complex was measured from the DNA circular dichroism spectrum. The ratio of Z to B-DNA is a linear function of polyarginine concentration and is sensitive to proteolytic digestion by trypsin. These results suggest that arginine-rich proteins may stabilize Z-DNA in vivo.