Deubiquitinase that antagonizes the anaphase-promoting complex (APC/C) during G1/S transition by mediating deubiquitination of cyclin-A (CCNA1 and CCNA2), thereby promoting S phase entry. Specifically mediates deubiquitination of 'Lys-11'-linked polyubiquitin chains, a specific ubiquitin-linkage type mediated by the APC/C complex. Also mediates deubiquitination of 'Lys-48'-linked polyubiquitin chains in vitro. Phosphorylation at Ser-628 during G1/S phase maximizes the deubiquitinase activity, leading to prevent degradation of cyclin-A (CCNA1 and CCNA2). Plays an important role in the regulation of DNA replication by stabilizing the licensing factor CDT1. Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). Interacts with FZR1/CDH1. Interacts with CDT1. The KEN box 3 is required for interaction with FZR1/CDH1 and is essential for APC(CDH1)-mediated ubiquitination. Polyubiquitinated via 'Lys-11'-linked ubiquitin by the APC(CDH1) complex during late mitosis, leading to its degradation. Able to mediate auto-deubiquitination. Phosphorylated at Ser-631 by CDK2 during G1/S phase but not during mitosis; phosphorylation at Ser-631 is required for deubiquitinase activity. Also polyubiquitinated during early G1 phase, without leading to degradation. Belongs to the peptidase C19 family.