| Abstract: | 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. |
