DNA supercoiling in apoptotic chromatin.
In a previous paper, we have reported that in rat thymocyte apoptosis chromatin undergoes a specific structural change as well as an appreciable increase in the unacetylated forms of histones H3 and H4. Here, we show that H3 and H4 deacetylation bears no relation to chromatin condensation, and present new ultrastructural and topological observations that largely clarify the organization of the condensed state. The texture of the latter corresponds to a closely woven network of negatively supercoiled 11 nm fibers, as shown by both ultrastructural observations and relaxation experiments using ethidium bromide. Circularly closed chromatin loops undergoing apoptotic condensation, clearly showing nucleosome compact dimers or higher oligomers, as well as long stretches of supercoiled DNA, have also been detected. All of these modifications are strongly reminiscent of the alterations induced in nucleosome bearing plasmids by the chromatin remodeling factors SWI/SNF and RSC.
D'Arrigo
Cristina
C
Istituto per lo Studio delle Macromolecole, Sezione di Genova, Via De Marini, 6 16146 Genoa, Italy.
Barboro
Paola
P
Mormino
Michele
M
Coradeghini
Rosella
R
Parodi
Silvio
S
Patrone
Eligio
E
Balbi
Cecilia
C
D000818:Animals; D017209:Apoptosis; D002478:Cells, Cultured; D002843:Chromatin / Q000648:ultrastructure*; D004278:DNA, Superhelical / Q000648:ultrastructure*; D006657:Histones / Q000378:metabolism; D051381:Rats; D013950:Thymus Gland / Q000166:cytology / Q000648:ultrastructure
D002843:Chromatin; D004278:DNA, Superhelical; D006657:Histones