The absence of histone Hl from the chromatin fraction obtained by sonication of calf thymus nuclei under "quasiphysiological" ionic conditions

Abstract

The minor chromatin fraction was isolated from the sonicated calf thymus nuclei on the basis of its differential solubility in the "quasiphysiological" salt medium (0.1 M KCl-0.05 M NaCl-l mM MgCl2-1 mM CaCl2). Histone Hl is almost completely absent from this fraction. DNA isolated from this fraction occurs in three discrete low mol. wt. fragments. The fraction of chromatin which lacks histone Hl can also be obtained by two other methods. On of them consists in salt precipitation of the chromatin gel and its subsequent sonication. The second method includes precipitation of the sonicated chromatin gel by salts. In the first case the properties of the chromatin fraction which remains in the supernatant after centrifugation closely resemble those of the original salt-soluble nuclear fraction. The second method yields supernatant fraction also lacking histone Hl but containing heterogeneous DNA. Comparisons were also made of the sonically-solubilized nuclear fractions obtained in the complete salt medium and its mono and divalent cationic constituents.

Effect of histone H1 removal on the distribution of ultraviolet-induced deoxyribonucleic acid repair synthesis within chromatin

“…Although the exact role(s) of histone HI in the packaging of DNA in chromatin is (are) not known, a number of studies suggest that it may be involved in higher order packaging (or condensation) of nucleosomes (Littau et al, 1965;Mirsky et al, 1968;Bradbury et al, 1973;Oudet et al, 1975;Lewis et al, 1976;Noll & Kornberg, 1977;Renz et al, 1977;Thoma & Roller, 1977Griffith & Christiansen, 1977;Keller et al, 1977;Gaubatz et al, 1977;Thoma et al, 1979). Also, HI appears to be much less prevalent in regions of chromatin undergoing transcription (Simpson & Reeck, 1973; Shirley & Anderson, 1976;Lishanskaya & Mosevitsky, 1976;Lau & Ruddon, 1977; Chiu et al, 1977;Letnansky, 1978;Djondjurov et al, 1979;Levy et al, 1979), and during replication, HI appears to associate with the daughter strand after (and separate from) the core histones (Worcel et al, 1978). These observations suggest that histone HI may be responsible for the packaging of nucleosomes in regions of chromatin where DNA is not being "actively processed" and that HI can bind and, perhaps, refold the nucleosome unit following a processing event.…”