✦ The story
Janus (after the Roman two-faced god, guardian of thresholds) is one of the ten anti-phage systems identified in 2018 by the Sorek team's bioinformatic screen. What was extraordinary at the time is that it works — the bacteria carrying it resist the phages tested — but nobody had the slightest idea how. The system is compact, its genes don't resemble anything known, and there is no obvious catalytic domain. Eight years later, in 2026, the molecular mechanism remains partially characterized: we know which genes are required, we know there is probably a sensor and an effector, but the exact coupling is still waiting for its crystallographer or cryo-electron microscopist. It is precisely the kind of orphan system that the 2026 Pasteur atlas surfaces by the thousands.
Discovered 2018
By Doron S., Melamed S., Ofir G., Sorek R. et al. (Weizmann Institute) — *Science* 359 (2018)
★ Why we care
Janus is an orphan mechanism to be characterized. Its value in Bactaegion is not directly translational — it's too early — but educational and strategic: it reminds us that among the 478,206 candidate families in the Pasteur atlas, the vast majority looks like Janus, not like CRISPR. Identified, but unknown. That is where the community annotation effort becomes meaningful: each additional characterization is one less Janus, and therefore one more mechanism available for pharmacology.
◇ The detail that lands
The name Janus aptly captures the epistemic status of the system: one face turned toward what we have seen (annotated genes, phenotypic resistance profile), one face turned toward what we don't yet know (molecular mechanism). Among the 28 cabinet dossiers, Janus is one of three (along with DRAPER and Shedu) that honestly acknowledges this ambiguity — we have not invented a narrative we cannot source.
