The Boi1 protein and its functionally redundant homolog Boi2p have been implicated in actin cytoskeleton reorganization and establishment of cell polarity (4, 5). boi1 boi2 double mutant cells become large and round or lyse with buds, displaying defects in bud formation and in the maintenance of cell polarity (5). Both Boi1p and Boi2p contain SH3, pleckstrin homology (PH), and proline-rich domains. (4, 5) Several structure/function and genetic analysis experiments have been done to determine which domains are important for interactions with other proteins involved in these processes. (4, 5, 6, 7) These studies showed that the Boi proteins interact physically and/or genetically with Bem1p, another SH3 domain protein, as well as three Rho-type GTPases: Cdc42p, Rho3p and the Rho3-related Rho4p (4, 5, 6, 7).

Rho3p/Rho4p interactions: Overexpression of either Rho3p or Rho4p suppresses the synthetic lethality of the boi1 boi2 mutations (4, 5).

Bem1p interactions: Two-hybrid analysis revealed that the proline-rich region of the Boi proteins mediates the interaction with the second SH3 domain of Bem1p (4, 5). Expressing the Boi1 protein with mutations in the proline-rich region suppresses boi1 boi2 double mutants as well as boi1 boi2 bem1 triple mutants (4).

Cdc42p interactions: The PH domain of the Boi proteins is necessary and sufficient for function and mediates the interaction with Cdc42p in the two-hybrid system (4). Additional two-hybrid experiments with Cdc42p point mutants suggest that the Boi proteins interact with the GTP-bound Cdc42p (4). Cells overexpressing Boi1p or Boi2p arrest as large, unbudded cells; cooverexpression of Cdc42p suppresses this defect (5, 8, 4)

Last updated: 1999-04-29