Structural and dynamic functions establish chromatin domains.
Kojiro Ishii (1), Clayton Lin (2), Ghislaine Arib (2), Ulrich K.
Laemmli (2)
(1) Division of Cell Biology, Institute of Life Science,
Kurume University, 2432-3 Aikawa-machi, Kurume, Fukuoka 839-0861, Japan;
(2) Molecular Biology, University of Geneva, 30 Quai Ansermet, Geneva,
1211, Switzerland (clayton.lin@molbio.unige.ch)
Drosophila and mammalian proteins protect
genes from heterochromatic repression in Saccharomyces cerevisiae
by two different mechanisms. Factors termed genuine boundary activities
(BAs) establish a structural, unidirectional bulwark against
heterochromatin. In contrast, factors termed desilencing activities
(DAs) act by the formation of a bidirectional, euchromatic island that
blocks spreading of heterochromatin. The Drosophila boundary
protein BEAF and, unexpectedly, the mammalian factor Sp1 exhibited a
robust BA in yeast. In contrast, mammalian CTCF, Drosophila GAGA
factor, yeast Gcn5p, and many mammalian transcription factors, although
inactive as upregulators of nonsilenced genes, work as DAs. DAs but not
BAs protect telomere-linked genes from silencing, presumably due to
looping of telomeres and ensuing multidirectional silencing. The data
demonstrate that ''genetic autonomy'' of chromatin domains is
established by both passive and active mechanisms.