# NAA15 (Q9BXJ9) research notes

## Summary
NAA15 (N-alpha-acetyltransferase 15, NatA auxiliary subunit; also NARG1, NATH, Tubedown-1) is the large, non-catalytic auxiliary subunit of the NatA N-terminal acetyltransferase complex. It dimerizes with the catalytic subunit NAA10, where its TPR-repeat-rich solenoid wraps around NAA10, anchoring the complex to the ribosome near the exit tunnel and orienting nascent polypeptide N-termini for co-translational acetylation. NAA15 itself has no acetyltransferase catalytic activity; rather it activates and confers ribosomal targeting and substrate specificity on NAA10, and is required for NatA-type N-terminal acetylation in vivo. It also serves as the scaffold for the NatA-associated factors HYPK and NAA50 (forming NatE). NAA15 is predominantly cytoplasmic with a nuclear pool, and a nuclear NAA15-containing complex with the Ku70/Ku80 (XRCC6/ XRCC5) heterodimer has been reported to up-regulate transcription from the osteocalcin promoter. NAA15 (as Tubedown-1) has additional reported roles in endothelial/retinal vascular biology, and NAA15 variants are associated with neurodevelopmental and congenital heart phenotypes.

## Core functions (from review)
- **GO:0010698 acetyltransferase activator activity** — Non-catalytic auxiliary subunit of the NatA N-terminal acetyltransferase complex that binds and activates the catalytic subunit NAA10, conferring N-terminal substrate specificity and serving as the scaffold for the NatA-associated factors HYPK and NAA50.
- **GO:0043022 ribosome binding** — Anchors the NatA complex to the ribosome near the polypeptide exit tunnel, enabling co-translational N-terminal acetylation of nascent chains.

## Provenance
Research and verbatim supporting quotes are recorded inline in `NAA15-ai-review.yaml` (per-annotation `supported_by` and `references` findings). This notes file summarizes the completed review; see the YAML for evidence citations.