Electric birefringence of chromatin reconstituted with various histone H1 subfractions

Rat liver chromatin is stripped of H1 histone by exposure to 0.5 M NaCl and reassociated with individual purified subfractions of H1 by salt-step dialysis. The effectiveness of proteins H1-1 and H1 in the condensation of DNA is monitored by transient electric birefringence and circular dichroism. Steady-state birefringence and relaxation time measurements show that reconstitutions are not perfect although some features of native chromatin are restored when a ratio of 2 moles of H1 per nucleosome is used. The amplitude of the positive birefringence is better recovered with H1-1 than with H1 but the values of relaxation times and molar ellipticities indicate that reconstituted samples exhibit a more compact and rigid structure compared to that of native chromatin.