A. Schmidt et al., THE YEAST PHOSPHATIDYLINOSITOL KINASE HOMOLOG TOR2 ACTIVATES RHO1 ANDRHO2 VIA THE EXCHANGE FACTOR ROM2, Cell, 88(4), 1997, pp. 531-542
The Saccharomyces cerevisiae phosphatidylinositol kinase homolog TOR2
is required for organization of the actin cytoskeleton. Overexpression
of RHO1 or RHO2, encoding Rho-like GTPases, or ROM2, encoding a GDP/G
TP exchange factor for RHO1 and RHO2, suppresses a tor2 mutation. Dele
tion of SAC7, a gene originally identified as a suppressor of an actin
mutation, also suppresses a tor2 mutation. SAC7 is a novel GTPase-act
ivating protein for RHO1. ROM2 exchange activity is reduced in a tor2
mutant, and overexpression of ROM2 lacking its PH domain can no longer
suppress a tor2 mutation. Thus, TOR2 signals to the actin cytoskeleto
n through a GTPase switch composed of RHO1, RHO2, ROM2, and SAC7. TOR2
activates this switch via ROM2, possibly via the ROM2 PH domain.