ISWI

ISWI refers to a family of ATP-dependent chromatin remodeling factors first identified in Drosophila as the Imitation Switch (ISWI) protein. Members belong to the SNF2 family of ATPases and use energy from ATP hydrolysis to reposition nucleosomes, thereby altering DNA accessibility and chromatin structure.

In humans, two catalytic ISWI ATPases are SMARCA5 (also called SNF2H) and SMARCA1 (SNF2L). These enzymes form several multi-subunit remodeling complexes through interactions with accessory proteins such as Acf1, BPTF, and WSTF. The complexes include ACF and CHRAC, RSF, and WICH, among others. Each complex carries out distinct remodeling tasks, such as nucleosome assembly and spacing, or targeted remodeling at specific genomic loci.

ISWI remodelers slide and space nucleosomes, influence chromatin compaction, and thereby regulate transcription, DNA replication, and repair. They often act to create regular nucleosome arrays and to modulate accessibility at promoters and enhancers. Their activity is regulated by complex composition, post-translational modifications, and interactions with histone tails and transcription factors.

Disruptions to ISWI-containing complexes have been linked to developmental abnormalities and cancer in various organisms; ongoing research seeks to clarify their roles in gene regulation, chromatin architecture, and genome stability.