PAS domains are involved in many signalling proteins where they are used as a signal sensor domain [1]. PAS domains appear in archaea, bacteria and eukaryotes. Several PAS-domain proteins are known to detect their signal by way of an associated cofactor. Heme, flavin, and a 4-hydroxycinnamyl chromophore are used in different proteins. This domain recognises oxygen and CO (Matilla et al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1. https://doi.org/10.1093/femsre/fuab043).

1: PAS domains: internal sensors of oxygen, redox potential, and light. Taylor BL, Zhulin IB; Microbiol Mol Biol Rev. 1999;63:479-506. PMID:10357859