Conserved domains control heterochromatin localization and silencing properties of SU(VAR)3–7

Abstract

The Drosophila protein SU(VAR)3-7 is essential for fly viability, chromosome structure, and heterochromatin formation. We report that searches in silico and in vitro for homologues of SU(VAR)3-7 were successful within, but not outside, the Drosophila genus. Protein sequence homology between the distant sibling species Drosophila melanogaster and Drosophila virilis is low, except for the general organization of the protein and three conserved motives: seven widely spaced zinc fingers in the N-terminal half and the BESS and BoxA motives in the C-terminal half of the protein. We have undertaken a fine functional dissection of SU(VAR)3-7 in vivo using transgenes encoding truncations of the protein. BESS mediates interaction of SU(VAR)3-7 with itself, and BoxA is required for specific heterochromatin association. Both are necessary for the silencing properties of SU(VAR)3-7. The seven zinc fingers, widely spaced over the N-terminal half of SU(VAR)3-7, are required for binding to polytene chromosomes. One finger is necessary and sufficient to determine the appropriate chromatin association of the C-terminal half of the protein. Conferring a function to each of the conserved motives allows us to better understand the mode of action of SU(VAR)3-7 in triggering heterochromatin formation and subsequent genomic silencing.

A Distinct Type of Heterochromatin Within Drosophila melanogaster Chromosome 4

“…Variegating reporters in distal chromosome 4 and pericentric regions respond differently to certain modifiers of PEV: Mod(var) mutations were used to investigate which components distinguish pericentric and distal fourth PEV. Recent studies suggest separable effects of SU(VAR)3-7 subdomains on PEV within different heterochromatic regions (Bushey and Locke 2004;Jaquet et al 2006). We find that mutations in both the C-terminal and Zn finger domains P43 and Su(var)3-7 P12 , respectively] greatly diminish silencing of pericentric and distal fourth chromosome P reporters (Figure 2).…”

JIL-1 and Su(var)3-7 Interact Genetically and Counteract Each Other's Effect on Position-Effect Variegation in Drosophila

“…Su(var)3-9 has been shown to catalyze most of the dimethylation of the histone H3K9 residue which in turn can promote HP1a and Su(var)3-7 recruitment (Schotta et al 2002;Jaquet et al 2006). In addition, Su(var)3-9, HP1a, and Su(var)3-7 can directly interact with each other, suggesting a model where interdependent interactions between Su(var)3-9, HP1a, and Su(var)3-7 lead to heterochromatin assembly at pericentric sites (Lachner et al 2001;Schotta et al 2002;Elgin and Grewal 2003;Jaquet et al 2006). Heterochromatin formation in Drosophila is initiated early in development through active removal of H3K4 methylation by the LSD1 demethylase homolog Su(var)3-3 (Rudolph et al 2007).…”

Combining Genetic Perturbations and Proteomics to Examine Kinase-Phosphatase Networks in Drosophila Embryos

“…The BESS motif is likely the region that interacts with Wee given that this domain facilitates protein-protein interactions (Bhaskar and Courey, 2002) and is often found together with the myb/SANT domain. The BESS motif of Suppressor of variegation 3–7 (Su(var)3–7) is required for its chromatin silencing properties (Jaquet et al, 2006). Like Su(var)3–7, Stwl influences trimethylation of HH3 at Lys9, in addition to Lys27 at larval stages (Yi et al, 2009).…”