Functional regions in the tubby family proteins. (a) Ribbon diagram of the tubby domain from Tub . Helices and β sheets are depicted as cylinders and arrows, respectively. The structure consists of a 12-stranded β barrel filled by a central hydrophobic helix. (b) Co-crystal structure of the tubby domain from Tub bound to GPMI-P2, a soluble analog of the head group from PIP2 . The PIP2 analog is shown in a van der Waals sphere representation. The PIP2 analog binds at a site on the tubby β-barrel adjacent to helix 6A. Panels (a) and (b) reproduced with permission from  and , respectively. (c) TULP3 binds to the IFT-A complex. A summary cartoon of the IFT-A complex subunits and their association with TULP3 is shown. The black dotted line encircles the 'core' complex subunits, and the blue dashed line contains the accessory subunits. TULP3 associates with the 'core' IFT-A complex, and this interaction is dependent on an amino-terminal region conserved between TULP3, TUB and TULP2. TPR, tetratricopeptide repeat.