Structure of the SANT domain from the Xenopus chromatin remodeling factor ISWI

Abstract

The SANT (Swi3, Ada2, N-Cor, and TFIIIB) module was first described as a putative DNA-binding domain with strong similarity to the helix-turn-helix DNA binding domain of Myb-related proteins.1–3 The X-ray structure of the C-terminal one third portion of the ATPase ISWI of Drospohila melanogaster, containing both SANT and SLIDE (SANT-Like ISWI Domain), confirmed the overall helix-turn-helix structural architecture of SANT as well as SLIDE.4 However, the DNA-contacting residues in Myb are not conserved in SANT and the structurally corresponding residues in the ISWI SANT domain are acidic, and therefore incompatible with DNA interaction. Recent studies suggested that SANT domains might be a histone-tail-binding module,5 including the DNA binding SANT domain of c-Myb.6 Here we present the X-ray structure of Xenopus laevis ISWI SANT domain, derived from limited proteolysis of a C-terminal fragment of ISWI protein.