<p>The PAS fold corresponds to the structural domain that has previously been defined as PAS and PAC motifs [<cite idref="PUB00014500"/>]. The PAS fold appears in archaea, eubacteria and eukarya. The PAS domain contains a sensory box, or S-box domain that occupies the central portion of the PAS domain but is more widely distributed. It is often tandemly repeated. Known prosthetic groups bound in the S-box domain include haem in the oxygen sensor FixL [<cite idref="PUB00033218"/>], FAD in the redox potential sensor NifL [<cite idref="PUB00033219"/>], and a 4-hydroxycinnamyl chromophore in photoactive yellow protein [<cite idref="PUB00033220"/>]. Proteins containing the domain often contain other regulatory domains such as response regulator or sensor histidine kinase domains. Other S-box proteins include phytochromes and the aryl hydrocarbon receptor nuclear translocator. </p><p>This domain has been found in the gene product of the madA gene of the filamentous zygomycete fungus <taxon tax_id="4837">Phycomyces blakesleeanus</taxon>. It has been shown that MadA encodes a blue-light photoreceptor for phototropism and other light responses. The gene is involved in the phototropic responses associated with sporangiophore growth; they exhibit phototropism by bending toward near-UV and blue wavelengths and away from far-UV wavelengths in a manner that is physiologically similar to plant phototropic responses [<cite idref="PUB00033221"/>].</p> PAS fold-3