[3][4][5] Due to this sensing capability, the PAS domain has been shown as the key structural motif involved in protein-protein interactions of the circadian clock, and it is also a common motif found in signaling proteins, where it functions as a signaling sensor.

[11] In 1998, the PAS domain core architecture was first characterized in the structure of photoactive yellow protein (PYP) from Halorhodospira halophila.

[5] The PAS domains that are known share less than 20% average pairwise sequence identity, meaning they are surprisingly dissimilar.

[14] The circadian clock that is currently understood for mammals begins when light activates BMAL1 and CLK to bind via their PAS domains.

They are present in plant and cyanobacterial phytochromes, vertebrate and invertebrate cGMP-stimulated phosphodiesterases (PDEs) and some non-photosynthetic eubacteria.

[22] They are common to animal calcium (Ca2+) channel subunits and certain prokaryotic chemotaxis receptors and play a role in small-molecule recognition across various species, suggesting a conserved mechanism of ligand binding.

[23] As opposite to the intracellular PAS and GAF domains, they show a long extra N-terminal alpha helix.