title: Evolutionary conservation and predicted structure of the Drosophila extra sex combs repressor protein.
abstract: The Drosophila extra sex combs (esc) protein, a member of the Polycomb group (PcG), is a transcriptional repressor of homeotic genes. Genetic studies have shown that esc protein is required in early embryos at about the time that other PcG proteins become engaged in homeotic gene repression. The esc protein consists primarily of multiple copies of the WD repeat, a motif that has been implicated in protein-protein interaction. To further investigate the domain organization of esc protein, we have isolated and characterized esc homologs from divergent insect species. We report that esc protein is highly conserved in housefly (72% identical to Drosophila esc), butterfly (55% identical), and grasshopper (56% identical). We show that the butterfly homolog provides esc function in Drosophila, indicating that the sequence similarities reflect functional conservation. Homology modeling using the crystal structure of another WD repeat protein, the G-protein beta-subunit, predicts that esc protein adopts a beta-propeller structure. The sequence comparisons and modeling suggest that there are seven WD repeats in esc protein which together form a seven-bladed beta-propeller. We locate the conserved regions in esc protein with respect to this predicted structure. Site-directed mutagenesis of specific loops, predicted to extend from the propeller surface, identifies conserved parts of esc protein required for function in vivo. We suggest that these regions might mediate physical interaction with esc partner proteins.
authors.affiliation: Department of Biochemistry, University of Minnesota, St. Paul 55108, USA.
authors.forename: J
authors.initials: J
authors.lastname: Ng
authors.forename: R
authors.initials: R
authors.lastname: Li
authors.forename: K
authors.initials: K
authors.lastname: Morgan
authors.forename: J
authors.initials: J
authors.lastname: Simon
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002080:Butterflies / Q000235:genetics; D003001:Cloning, Molecular; D003198:Computer Simulation; D017124:Conserved Sequence; D018076:DNA, Complementary / Q000235:genetics; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D029721:Drosophila Proteins; D019143:Evolution, Molecular; D006110:Grasshoppers / Q000235:genetics; D011495:Histone-Lysine N-Methyltransferase; D006793:Houseflies / Q000235:genetics; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D063150:Polycomb Repressive Complex 1; D063151:Polycomb Repressive Complex 2; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
chemical_list: D018076:DNA, Complementary; D029721:Drosophila Proteins; D019476:Insect Proteins; C066770:Pc protein, Drosophila; D012097:Repressor Proteins; D011495:Histone-Lysine N-Methyltransferase; D063151:Polycomb Repressive Complex 2; C543389:esc protein, Drosophila; D063150:Polycomb Repressive Complex 1