HIGH-AFFINITY BINDING-SITES FOR HISTONE H1 IN PLASMID DNA

The interaction of histone H1 isolated from chicken erythrocytes with restriction fragments from plasmids pBR322 and pUC19 was studied by ge l electrophoresis. Certain restriction fragments exhibited unusually h igh affinity for the histone, forming high molecular mass complexes at protein to DNA ratios at which the other fragments did not show evide nce for binding. The highly preferred fragments are intrinsically curv ed, as judged by their electrophoretic mobility in polyacrylamide gels , by computer modeling, and by imaging with scanning force microscopy. However, control experiments with either curved portions of the same fragments or highly curved kinetoplast DNA fragments showed that the p resence of curvature alone was not sufficient for preferential binding . By using various restriction fragments centered around the highly pr eferred sequence, it was found that the high-affinity binding required in addition the presence of specific sequences on both sides of the r egion of curvature. Thus, both curvature and the presence of specific sites seem to be required to generate high affinity.