RHO1P-BNI1P-SPA2P INTERACTIONS - IMPLICATION IN LOCALIZATION OF BNI1PAT THE BUD SITE AND REGULATION OF THE ACTIN CYTOSKELETON IN SACCHAROMYCES-CEREVISIAE
T. Fujiwara et al., RHO1P-BNI1P-SPA2P INTERACTIONS - IMPLICATION IN LOCALIZATION OF BNI1PAT THE BUD SITE AND REGULATION OF THE ACTIN CYTOSKELETON IN SACCHAROMYCES-CEREVISIAE, Molecular biology of the cell, 9(5), 1998, pp. 1221-1233
Rho1p is a yeast homolog of mammalian RhoA small GTP-binding protein.
Rho1p is localized at the growth sites and required for bud formation.
We have recently shown that Bni1p is a potential target of Rho1p and
that Bni1p regulates reorganization of the actin cytoskeleton through
interactions with profilin, an actin monomer-binding protein. Using th
e yeast two-hybrid screening system, we cloned a gene encoding a prote
in that interacted with Bni1p. This protein, Spa2p, was known to be lo
calized at the bud tip and to be implicated in the establishment of ce
ll polarity. The C-terminal 254 amino acid region of Spa2p, Spa2p(1213
-1466), directly bound to a 162-amino acid region of Bni1p, Bni1p(826-
987). Genetic analyses revealed that both the bni1 and spa2 mutations
showed synthetic lethal interactions with mutations in the genes encod
ing components of the Pkc1p-mitogen-activated protein kinase pathway,
in which Pkc1p is another target of Rho1p. Immunofluorescence microsco
pic analysis showed that Bni1p was localized at the bud tip in wild-ty
pe cells. However, in the spa2 mutant, Bni1p was not localized at the
bud tip and instead localized diffusely in the cytoplasm. A mutant Bni
1p, which lacked the Rho1p-binding region, also failed to be localized
at the bud tip. These results indicate that both Rho1p and Spa2p are
involved in the localization of Bni1p at the growth sites where Rho1p
regulates reorganization of the actin cytoskeleton through Bni1p.