The globular domain of histone H1 is sufficient to direct specific gene repression in early Xenopus embryos.
One molecule of a linker histone such as histone H1 is incorporated into every metazoan nucleosome [1]. Histone H1 has three distinct structural domains: the positively charged amino-terminal and carboxy-terminal tails are separated by a globular domain that is similar to the winged-helix motif found in sequence-specific DNA-binding proteins [2]. The globular domain interacts with DNA immediately contiguous to that wrapped around the core histones [3,4], whereas the tail domains are important for the compaction of nucleosomal arrays [5]. Experiments in vivo indicate that histone H1 does not function as a global transcriptional repressor, but instead has more specific regulatory roles [6-9]. In Xenopus, maternal stores of the B4 linker histone that are assembled into chromatin during the early cleavage divisions are replaced by somatic histone H1 during gastrulation [10]. This transition in chromatin composition causes the repression of genes encoding oocyte-type 5S rRNAs, and restricts the competence of ectodermal cells to differentiate into mesoderm [6,9-11]. Here, we demonstrate that the globular domain of histone H1 is sufficient for directing gene-specific transcriptional repression and for restricting the mesodermal competence of embryonic ectoderm. We discuss our results in the context of specific structural roles for this domain in the nucleosome.
Vermaak
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Laboratory of Molecular Embryology National Institute of Child Health and Human Development NIH Building 18T, Room 106, Bethesda, Maryland, 20892-5431, USA.
Steinbach
O C
OC
Dimitrov
S
S
Rupp
R A
RA
Wolffe
A P
AP
D000818:Animals; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D006657:Histones / Q000502:physiology*; D017434:Protein Structure, Tertiary; D014981:Xenopus / Q000196:embryology / Q000235:genetics*
D006657:Histones