The SARAH (Sav/Rassf/Hpo) domain is found at the C terminus in three classes of eukaryotic tumour suppressors that give the domain its name. In the Sav (Salvador) and Hpo (Hippo) families, the SARAH domain mediates signal transduction from Hpo via the Sav scaffolding protein to the downstream component Wts (Warts); the phosphorylation of Wts by Hpo triggers cell cycle arrest and apoptosis by down-regulating cyclin E, Diap 1 and other targets [, ]. The SARAH domain is also involved in dimerisation, as in the human Hpo orthologue, Mst1, which homodimerises via its C-terminal SARAH domain. The SARAH domain is found associated with other domains, such as protein kinase domains, WW/rsp5/WWP domain (), C1 domain (), LIM domain (), or the Ras-associating (RA) domain ().This entry represents the C-terminal SARAH domain of Mst1. The Mst1 SARAH domain interacts with Rassf1 and Rassf5 by forming a heterodimer which mediates the apoptosis process [].