A comparative X‐ray study of a nucleoprotamine and DNA complexes with polylysine and polyarginine

The high‐humidity X‐ray pattern of oriented fibers prepared from salmon spermheads strongly resembles that of DNA in the B form. However, the nucleoprotamine pattern has a more intense first layer line and increased lateral unit‐cell dimensions. Complexes of DNA with poly‐ L ‐lysine and poly‐ L ‐arginine were prepared and photographed at various relative humidities. The most crystalline patterns were obtained at 92% and also indicate DNA in the B form. However, whereas polylysine–DNA, like the spermheads, has a primitive hexagonal cell, polyarginine–DNA, like NaDNA, has three molecules in the unit cell. Polylysine–DNA, but not polyarginine–DNA, also resembles spermheads in having a strong first layer line. All three complexes show increasing intermolecular distance with increasing humidity, but with sharp maxima when photographed in water, which indicates cross‐linking between the molecules. Lowering the humidity causes the polylysine–DNA, but not polyarginine–DNA, to change conformation from the B to the C form. The structural implications of these results are discussed in the light of model‐building studies and a comparison of calculated and observed X‐ray intensities.