The function of UBLCP1 (ubiquitin like domain containing CTD phosphatase 1, Ensembl gene identifier ENSG00000164332) is as follows. Dephosphorylates 26S nuclear proteasomes, thereby decreasing their proteolytic activity (PubMed:21949367, PubMed:28539385). Recruited to the 19S regulatory particle of the 26S proteasome through its interaction with 19S component PSMD2/RPN1 (PubMed:28539385). Once recruited, dephosphorylates 19S component PSMC2/RPT1 which impairs PSMC2 ATPase activity and disrupts 26S proteasome assembly (PubMed:28539385). Has also been reported to stimulate the proteolytic activity of the 26S proteasome (PubMed:32071216). {ECO:0000269|PubMed:21949367, ECO:0000269|PubMed:28539385, ECO:0000269|PubMed:32071216}.