This protein is found in a wide range of eukaryotes. It is a nuclear protein previously suggested to be DNA binding [1,2] but recent studies suggest that they play a role in the spliceosome complex [3]. In plants, this family is essential for correct circadian clock functioning by acting as a light-quality regulator coordinating the activities of blue and red light signalling pathways during plant growth - inhibiting growth in red light but promoting growth in blue light [4]. The AlphaFold model of this domain shows structural similarity to the RA domain Pfam:PF00788.

1: Differential expression of XAP5, a candidate disease gene. Mazzarella R, Pengue G, Yoon J, Jones J, Schlessinger D; Genomics 1997;45:216-219. PMID:9339379

2: Human and mouse XAP-5 and XAP-5-like (X5L) genes: identification of an ancient functional retroposon differentially expressed in testis. Sedlacek Z, Munstermann E, Dhorne-Pollet S, Otto C, Bock D, Schutz G, Poustka A; Genomics 1999;61:125-132. PMID:10534398

3: Mutations in FAM50A suggest that Armfield XLID syndrome is a spliceosomopathy. Lee YR, Khan K, Armfield-Uhas K, Srikanth S, Thompson NA, Pardo M, Yu L, Norris JW, Peng Y, Gripp KW, Aleck KA, Li C, Spence E, Choi TI, Kwon SJ, Park HM, Yu D, Do Heo W, Mooney MR, Baig SM, Wentzensen IM, Telegrafi A, McWalter K, Moreland T, Roadhouse C, Ramsey K, Lyons MJ, Skinner C, Alexov E, Katsanis N, Stevenson RE, Choudhary JS, Adams DJ, Kim CH, Davis EE, Schwartz CE; Nat Commun. 2020;11:3698. PMID:32703943

4: XAP5 CIRCADIAN TIMEKEEPER coordinates light signals for proper timing of photomorphogenesis and the circadian clock in Arabidopsis. Martin-Tryon EL, Harmer SL; Plant Cell. 2008;20:1244-1259. PMID:18515502