Finding. Mitochondrial outer membrane permeabilization (MOMP) does more than dump cytochrome c. The broken organelle gets a ubiquitin coat, and that coat turns on nuclear factor kappa B (NF-kappaB). Heilig, Tait and colleagues name the E3 ligase: RNF213. It is already famous for cell-autonomous immunity to intracellular bacteria. Here it is required for pro-inflammatory ubiquitination of mitochondria after MOMP. The chain type is M1-linked, meaning linear. The surprise is that this does not need the linear ubiquitin chain assembly complex (LUBAC), the textbook M1 writer. RNF213 can catalyze M1 linkages itself. Those mitochondrial M1 chains recruit NEMO, the essential NF-kappaB adaptor, and inflammation starts.
Why this paper matters
For a decade the field has treated permeabilized mitochondria as both a death switch and a dirty organelle. The missing sentence was which ligase writes the inflammatory code. Parkin-style coats are about mitophagy. LUBAC was the default guess for linear chains. This preprint splits those jobs. Pathogen defense and mitochondrial damage now share an enzyme, not just a metaphor.
That matters for antitumor immunity and senescence, the two places where inflammatory MOMP is supposed to do work. If RNF213 is the writer, those models get a handle you can delete.
How to read the score
Low nineties. A named E3, a non-canonical M1 route, a NEMO mechanism, and a clean mitochondrial frame. Confidence is high for the genetic requirement and the LUBAC-independence claim as stated. It is not high for physiology.
Caveats
Abstract-level only. We do not see the MOMP trigger, the cell panel, or whether caspases are blocked (the usual trick that lets inflammatory MOMP persist). Direct M1 catalysis by RNF213 needs the biochemical figure, not the sentence. Moyamoya-associated RNF213 alleles are not mapped here.
What to do with it
If you track mitochondrial inflammation, replace "LUBAC on mitochondria" with "RNF213, then NEMO." If you build post-MOMP screens, add RNF213 and M1-specific probes before you credit Parkin. Pull the linkage data before you write that linear ubiquitin on mitochondria is a LUBAC product.