ATP-dependent helicase involved mating type switching and in silencing interference through its interaction with the silencing regulator SIR4. Cooperates with UBC4 and UBC5 to mediate ubiquitination of SUMO conjugates. Interacts with CDC3, CDC11, EBP2, SIR4, UBC4 and SUMO/SMT3. Belongs to the SNF2/RAD54 helicase family.