## USP21
- **UniProt:** Q9UK80 · **batch:** proteostasis-batch-2026-06-07c · **review status:** COMPLETE
- **PN placement:** TR `Cytosolic translation|Ribosome-associated QC|Deubiquitination`; UPS `DUBs and UBL demodifiers|USP|other|other` ; **PN-node mapping:** RQC type→GO:0101005 deubiquitinase activity (mapped, ok_for_propagation); RQC group→GO:0006515 protein QC for misfolded/incompletely synthesized proteins (new_to_goa); UPS group→GO:0101005 (entailed_by_goa_closure); type/subtype/class/branch = no_mapping.
- **Consistency:** Consistent. Notes, review, and PN agree USP21 is a dual ubiquitin/NEDD8 cysteine-type DUB (GO:0004843, GO:0019784) that, per PMID:32011234, deubiquitinates 40S eS10/RPS10 and uS10/RPS20 to antagonize ZNF598 and limit RQC. The RQC role is captured in the review as GO:0016579 protein deubiquitination (IDA). MF-granularity note: PN projects GO:0101005 (parent) while GOA/review use child GO:0004843; "entailed_by_goa_closure" is the correct status, no conflict.
- **PN story / NEW pressure:** PN asserts an RQC process role. GOA/review for USP21 contain GO:0016579 but NOT the projected GO:0006515 (verified real, non-obsolete) nor any rescue/RQC-specific process term. Unlike ZNF598/USP10, USP21 has no GO:0072344 or GO:1990116. GO:0006515 (or the more specific GO:1990116 ribosome-associated ubiquitin-dependent protein catabolic process, verified real) is a defensible ADD: USP21's RQC role is a *negative* regulator (it reverses the mark), so a generic "involved_in protein QC" term is biologically defensible. Conclude: defensible ADD (broad), but the negative-regulator nuance means the bare process term slightly over-states; GO:0016579 already partly captures it.
- **Mapping strategy:** USP21 does not change the node. PN-projected GO:0006515 is broader than the review's GO:0016579/GO:0004843 — a "broader than review" case (cf. TOMM20/HSPA8 precedent). UPS group→GO:0101005 entailed by GOA closure (GO:0004843 child present). Status/scope correct.
- **Evidence alignment:** PN UPS row cites "19734957/rev" (Komander/Clague DUB review) — not in review references; the RQC TR row has no titled reference. Review's RQC evidence (PMID:32011234) is more specific and absent from the PN rows. Strong divergence: the key RQC paper is in the review but not cited by PN.
- **Verdict:** Consistent; RQC role captured via GO:0016579 (IDA). PN's GO:0006515 is a defensible-but-broader ADD; no NEW term required.