Abstract
Suppressor of Hairy-wing [Su(Hw)] is one of the best characterized architectural proteins in Drosophila and recruits the CP190 and Mod(mdg4)-67.2 proteins to chromatin, where they form a well-known insulator complex. Recently, HP1 and insulator partner protein 1 (HIPP1), a homolog of the human co-repressor Chromodomain Y-Like (CDYL), was identified as a new partner for Su(Hw). Here, we performed a detailed analysis of the domains involved in the HIPP1 interactions with Su(Hw)-dependent complexes. HIPP1 was found to directly interact with the Su(Hw) C-terminal region (aa 720–892) and with CP190, but not with Mod(mdg4)-67.2. We have generated Hipp1 null mutants (HippΔ1) and found that the loss of Hipp1 does not affect the enhancer-blocking or repression activities of the Su(Hw)-dependent complex. However, the simultaneous inactivation of both HIPP1 and Mod(mdg4)-67.2 proteins resulted in reduced CP190 binding with Su(Hw) sites and significantly altered gypsy insulator activity. Taken together, these results suggested that the HIPP1 protein stabilized the interaction between CP190 and the Su(Hw)-dependent complex.
Highlights
Insulators in Drosophila and vertebrate genomes have been identified based on their abilities to disrupt communications between enhancers and promoters, when inserted between them, and to prevent the repression mediated by heterochromatin[1,2,3,4,5]
We found that HP1 and insulator partner protein 1 (HIPP1) can form dimers through both its crotonase and N-terminal domains
Tests for the interactions between HIPP1 domains and the insulator proteins (Fig. 1c) showed that the N-terminal domain interacts with CP190, whereas the crotonase domain interacts with Su(Hw)
Summary
Insulators in Drosophila and vertebrate genomes have been identified based on their abilities to disrupt communications between enhancers and promoters, when inserted between them, and to prevent the repression mediated by heterochromatin[1,2,3,4,5]. Artificial Su(Hw) protein binding sites can block various enhancers during all stages of Drosophila development[29,30,31,32]. Only Su(Hw) binds to repressed promoters (SBS-O); the inactivation of either CP190 or Mod(mdg4)-67.2 does not affect fertility or the Su(Hw)-dependent repression of gene expression in the ovaries[28,35]. CP190 is involved in the recruitment of several complexes to SBS-C and SBS-CM sites, including the nucleosome remodeling factor (NURF), the dimerization partner, RB-like, E2F, and multi-vulval class B (dREAM), and the Spt-Ada-Gcn[5] acetyltransferase (SAGA) complexes, which are activators of gene transcription[44,45,46,47]
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