DNA recognition by β-sheets in the Arc represser–operator crystal structure

Abstract

TRANSCRIPTION of the ant gene during lytic growth of bacteriophage P22 (ref. 1) is regulated by the cooperative binding of two Arc repressor dimers to a 21-base-pair operator site2,3. Here we report the co-crystal structure of this Arc tetramer–operator complex at 2.6 Å resolution. As expected from genetic4–6 and structural studies7 and from the co-crystal structure of the homologous Escherichia coli MetJ repressor8, each Arc dimer uses an antiparallel ß-sheet to recognize bases in the major groove. However, the Arc and Met J complexes differ in several important ways: the (β-sheet–DNA interactions of Arc are far less symmetrical; DNA binding by Arc is accompanied by important conformational changes in the β-sheet; and Arc uses a different part of its protein surface for dimer–dimer interactions.