Protease that catalyzes two essential functions in the SUMO pathway: processing of full-length SMT3 to its mature form and deconjugation of SMT3 from targeted proteins. Has an essential role in the G2/M phase of the cell cycle. Hydrolysis of the alpha-linked peptide bond in the sequence Gly-Gly-|-Ala-Thr-Tyr at the C-terminal end of the small ubiquitin-like modifier (SUMO) propeptide, Smt3, leading to the mature form of the protein. A second reaction involves the cleavage of an epsilon-linked peptide bond between the C-terminal glycine of the mature SUMO and the lysine epsilon-amino group of the target protein. Present with 377 molecules/cell in log phase SD medium. Belongs to the peptidase C48 family.