Identification and Characterization of the Human Set1B Histone H3-Lys4 Methyltransferase Complex

Abstract

We previously identified a mammalian Set1A complex analogous to the yeast Set1/COMPASS histone H3-Lys4 methyltransferase complex (Lee, J. . Both Set1A and Set1B are widely expressed. Inducible expression of the carboxyl terminus of either Set1A or Set1B decreases steady-state levels of both endogenous Set1A and Set1B protein, but does not alter the expression of the non-catalytic components of the Set1 complexes. A 123-amino acid fragment upstream of the Set1A SET domain is necessary for interaction with CFP1, Ash2, Rbbp5, and Wdr5. This protein domain is also required to mediate feedback inhibition of Set1A and Set1B expression, which is a consequence of reduced Set1A and Set1B stability when not associated with the methyltransferase complex. Confocal microscopy reveals that Set1A and Set1B each localize to a largely non-overlapping set of euchromatic nuclear speckles, suggesting that Set1A and Set1B each bind to a unique set of target genes and thus make non-redundant contributions to the epigenetic control of chromatin structure and gene expression.

Efficient differentiation of murine embryonic stem cells requires the binding of CXXC finger protein 1 to DNA or methylated histone H3-Lys4

“…Another shared core component, Wdr5, associates with chromatin by interacting with methylated histone H3K4 to catalyze tri-methylation of K4 [35]. Finally, despite sharing these numerous chromatin-binding components, the Setd1a and Setd1b complexes exhibit nonoverlapping sub-nuclear distributions within euchromatin regions as observed by confocal immunofluorescence [7]. The Setd1a and Setd1b enzymes contain highly divergent central domains that may confer distinct genomic targeting behavior.…”

“…For example, the Setd1 complexes contain Wdr82 that is lacking in the other COMPASS-like complexes (MLL1-4) [7,11,40]. Wdr82 interacts with serine 5-phosphorylated C-terminal domain repeats of RNA polymerase II and recruits the Setd1a complex to the transcriptional start sites of active genes [41].…”

“…supplemented with 200 µg/ml hygromycin B was replaced every other day for fourteen days until individual colonies were isolated and expanded. These clones were assayed for expression of Cfp1 by western blotting using an antiserum against Cfp1 [7]. Only clones expressing Cfp1 protein > 50% of WT Cfp1 levels were chosen for further study.…”

“…Mammalian Setd1 histone lysine methyltransferase complexes (Setd1a/Setd1b) are euchromatin-specific enzyme complexes that, in addition to the MLL complexes (MLL 1-4), catalyze the methylation of histone H3K4 [6,7]. These complexes contain a catalytic SET [Su(var)3-9, Enhancer of Zeste, trithorax] domain and are analogous to the yeast Set1/COMPASS complex [8,9].…”

“…In addition to a unique catalytic subunit, the Setd1 and MLL histone H3K4 methyltransferase complexes all contain four common components; Ash2l, Wdr5, Dpy30, and Rbbp5 [10]. In addition, Setd1a/Setd1b complexes also contain Wdr82 and CXXC finger protein 1 (Cfp1) [7,11].…”