Order of assembly and protein–protein interactions of Ist1, Did2, Vta1, and Vps60 (see Discussion). Solid lines indicate interactions that we and others have shown (Babst et al., 2002a,b; Yeo et al., 2003; Scott et al., 2005a; Azmi et al., 2006; Lottridge et al., 2006; Nickerson et al., 2006; Vajjhala et al., 2006, 2007; Obita et al., 2007); dashed lines indicate interactions that require further investigation.