# DNAJC21 (Q5F1R6) research notes

J-domain (HSP40) co-chaperone of the HSP70 system acting in **ribosome biogenesis**,
specifically maturation of the large (60S) ribosomal subunit. Also named DNAJA5.

## Architecture
- N-terminal J-domain (HPD motif) that recruits/stimulates HSP70 ATPases.
- Two C2H2 zinc fingers within an otherwise disordered C-terminal region.
- Human counterpart of the yeast 60S-maturation J-protein Jjj1.

## Function / localization
- Localizes to cytoplasm, nucleus and especially the **nucleolus**; associates with
  precursor 45S rRNA. [UniProt Q5F1R6 subcellular location]
- Works with the HSP70 chaperone **HSPA8** and cofactors **PA2G4** (60S nuclear-export
  factor) and **ZNF622** to drive late nucleolar rRNA processing and cytoplasmic
  maturation/recycling of the 60S subunit. [PMID:27346687]

## Disease
- Biallelic loss-of-function variants cause a cancer-prone **bone marrow failure
  syndrome (BMFS3)**, Shwachman–Diamond-like — establishing DNAJC21 as a ribosomopathy
  gene. [PMID:27346687]

## Curation calls
- Core MFs: HSP70 (HSPA8) co-chaperone binding (GO:0051087) driving 60S maturation;
  RNA binding (GO:0003723) to precursor rRNA.
- Bare high-throughput `protein binding` to HTT/MTERF1 and domain-only nucleic-acid
  binding marked over-annotated; folding terms kept non-core (co-chaperone, not foldase).