Movement of histones in chromatin induced by shearing.

Methylation of accessible DNA within chromatin by restriction modification methylases from Haemophilus influenzae was used to detect movement of histones along the DNA strand during chromatin manipulation. Methylation at different stages of chromatin preparation was followed by titration of the nucleoprotein with ploy(D-lysine), digestion of chromosomal proteins with pronase and analysis of the DNA-poly(D-lysine) complex in steep cesium chloride gradients. Comparison of the specific radioactivities in the peak fractions of the free DNA and the DNA-poly(D-lysine) complex, respectively, reveals that lateral movement of histones, relative to specific sites in the DNA marked by restriction methylases, occurs during manipulation and fragmentation of chromatin.