The chromatin remodeling Isw1a complex is regulated by SUMOylation

Area of Science:

• * Molecular biology
• * Biochemistry
• * Genetics

Background:

• * The ISWI protein family are chromatin remodeling ATPases essential for eukaryotic gene regulation.
• * In yeast, Isw1 forms distinct complexes (Isw1a and Isw1b) with alternative subunits (Ioc2, Ioc3, Ioc4).
• * The regulation of Isw1's chromatin remodeling activity remains poorly understood.

Purpose of the Study:

• * To investigate the post-translational modifications regulating the chromatin remodeler Isw1.
• * To elucidate the functional consequences of Isw1 SUMOylation on its interaction with cofactors and chromatin recruitment.

Main Methods:

• * Identification of SUMOylation sites on Isw1 through site-directed mutagenesis.
• * Generation of a SUMO-defective Isw1 mutant.
• * Analysis of Isw1-Ioc3 complex formation and chromatin association.

Main Results:

• * Isw1 is extensively SUMOylated by Siz1/Siz2 E3 ligases, with limited deSUMOylation by Ulp1/Ulp2 proteases.
• * Key lysine residues mediating Isw1 SUMOylation were identified.
• * SUMOylation of Isw1 enhances its interaction with the Ioc3 cofactor, promoting Isw1-Ioc3 complex recruitment to chromatin.

Conclusions:

• * Post-translational SUMOylation represents a novel regulatory mechanism for the ISWI chromatin remodeler.
• * SUMOylation of Isw1 is crucial for its functional interaction with Ioc3 and efficient chromatin targeting.