Acts as an E3 ligase mediating SUMO/Smt3 attachment to septins and PCNA. May be involved in chromosome maintenance. Protein modification; protein sumoylation. Interacts with UBC9 and CDC3. Present at the bud neck in early M-phase. The SAP domain is required for nuclear targeting. The SP-RING-type zinc finger mediates interaction with UBC9 and CDC3 and is required for E3 activity. Phosphorylated in early M-phase. Autosumoylated upon ethanol stress. Present with 149 molecules/cell in log phase SD medium. Belongs to the PIAS family.