Abstract
The SWIRM domain is a novel module found in the Swi3 and Rsc8 subunits of SWI/SNF‐family chromatin remodeling complexes, and the Ada2 and BHC110/LSD1 subunits of chromatin modification complexes. We present the high‐resolution crystal structure of the SWIRM domain from Swi3 and characterize the in vitro and in vivo function of the SWIRM domains from Swi3 and Rsc8. The Swi3 SWIRM forms a novel 4‐helix bundle containing a psuedo 2‐fold axis, and a helix‐turn‐helix motif commonly found in DNA binding proteins. Notably, the Swi3 SWIRM binds free DNA and mononucleosomes with high and comparable affinity, attributes suited for nucleosome interaction. Genetic and biochemical studies also reveal that the Rsc8 and Swi3 SWIRM domains are essential for the proper assembly and in vivo functions of their respective complexes. Together, these studies identify the SWIRM domain as an essential multi‐functional module for the regulation of gene expression.