ULK1 (Unc-51-like autophagy-activating kinase 1)

Classification

Category: Downstream effector / autophagy-initiation kinase

Aliases: ATG1 homolog

Relationship to mTOR complexes: Direct mTORC1 substrate; downstream of mTORC1 — see mTORC1 vs mTORC2 for the full complex-level map.

Summary

ULK1 is a serine/threonine kinase that initiates autophagosome formation. Active mTORC1 phosphorylates ULK1 at inhibitory sites, SUPPRESSING autophagy initiation; when mTORC1 activity falls (e.g. nutrient restriction, rapamycin), ULK1 is de-repressed and can initiate autophagy. ULK1 phosphorylation state is a STATIC marker, not a direct flux measurement -- see the autophagic-flux page for why this distinction matters.

• mTORC1 (active) phosphorylates ULK1 at inhibitory residues, suppressing its kinase activity
• AMPK can directly phosphorylate ULK1 at activating residues, particularly when mTORC1 activity is low

• When de-repressed, ULK1 phosphorylates downstream autophagy-initiation machinery, promoting autophagosome nucleation

• ULK1 is one of the four downstream outputs of mTORC1 tracked in this dataset's pathway map (alongside S6K1, 4E-BP1, TFEB); it is the one specific to autophagy INITIATION rather than protein synthesis.
• ULK1 phosphorylation state (an assay readout) is a static snapshot and is NOT equivalent to measured autophagic flux -- see /autophagic-flux for the flux-vs-static-marker distinction that this dataset treats as a core editorial nuance.

Source tier

Tier 2 · Biological synthesis (author-cluster reviews, not primary trial data) Reference synthesis attributed in the brief to the Saxton & Sabatini; Laplante & Sabatini; and Liu & Sabatini mTOR review literature (author-cluster attribution, tier 2, brief §4). Exact article-level PMID/DOI not supplied in the sourcing brief and is not fabricated here.