Mouse polycomb proteins bind differentially to methylated histone H3 and RNA and are enriched in facultative heterochromatin.
The chromodomain (CD) of the Drosophila Polycomb protein exhibits preferential binding affinity for histone H3 when trimethylated at lysine 27. Here we have investigated the five mouse Polycomb homologs known as Cbx2, Cbx4, Cbx6, Cbx7, and Cbx8. Despite a high degree of conservation, the Cbx chromodomains display significant differences in binding preferences. Not all CDs bind preferentially to K27me3; rather, some display affinity towards both histone H3 trimethylated at K9 and H3K27me3, and one CD prefers K9me3. Cbx7, in particular, displays strong affinity for both H3K9me3 and H3K27me3 and is developmentally regulated in its association with chromatin. Cbx7 associates with facultative heterochromatin and, more specifically, is enriched on the inactive X chromosome. Finally, we find that, in vitro, the chromodomain of Cbx7 can bind RNA and that, in vivo, the interaction of Cbx7 with chromatin, and the inactive X chromosome in particular, depends partly on its association with RNA. We propose that the capacity of this mouse Polycomb homolog to associate with the inactive X chromosome, or any other region of chromatin, depends not only on its chromodomain but also on the combination of histone modifications and RNA molecules present at its target sites.
Bernstein
Emily
E
Laboratory of Chromatin Biology, The Rockefeller University, 1230 York Ave., New York, New York 10021, USA.
Duncan
Elizabeth M
EM
Masui
Osamu
O
Gil
Jesus
J
Heard
Edith
E
Allis
C David
CD
D000595:Amino Acid Sequence; D000818:Animals; D002843:Chromatin; D005260:Female; D006570:Heterochromatin / Q000378:metabolism*; D006657:Histones / Q000378:metabolism*; D008745:Methylation; D051379:Mice; D033681:Mitochondrial Membrane Transport Proteins; D008969:Molecular Sequence Data; D063150:Polycomb Repressive Complex 1; D063146:Polycomb-Group Proteins; D011485:Protein Binding; D012313:RNA / Q000378:metabolism*; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D013234:Stem Cells / Q000166:cytology
C570426:Cbx2 protein, mouse; D002843:Chromatin; D006570:Heterochromatin; D006657:Histones; D033681:Mitochondrial Membrane Transport Proteins; D063146:Polycomb-Group Proteins; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; C077885:XIST non-coding RNA; D012313:RNA; C570429:Cbx8 protein, mouse; D063150:Polycomb Repressive Complex 1