This domain is characteristic of cilia- and flagella-associated protein 20 (CFA20). CFA20 is a cilium- and flagellum-specific protein that plays a role in axonemal structure organisation and motility [1,2]. In Chlamydomonas reinhardtii, it stabilises outer doublet microtubules (DMTs) of the axoneme and may work as a scaffold for intratubular proteins, such as tektin and PACRG, to produce the beak structures in DMT1 [2,3]. Other proteins contain a domain with homology to CFA20. WDR90/POC16 contains such a domain in its N terminus, followed by a large C-terminal domain with multiple WD40 repeats [2]. This domain is also present in the N terminus of uncharacterised protein C3orf67.

1: Bug22p, a conserved centrosomal/ciliary protein also present in higher plants, is required for an effective ciliary stroke in Paramecium. Laligne C, Klotz C, de Loubresse NG, Lemullois M, Hori M, Laurent FX, Papon JF, Louis B, Cohen J, Koll F; Eukaryot Cell. 2010;9:645-655. PMID:20118210

2: FAP20 is an inner junction protein of doublet microtubules essential for both the planar asymmetrical waveform and stability of flagella in Chlamydomonas. Yanagisawa HA, Mathis G, Oda T, Hirono M, Richey EA, Ishikawa H, Marshall WF, Kikkawa M, Qin H; Mol Biol Cell. 2014;25:1472-1483. PMID:24574454

3: The conserved ciliary protein Bug22 controls planar beating of Chlamydomonas flagella. Meng D, Cao M, Oda T, Pan J; J Cell Sci. 2014;127:281-287. PMID:24259666