An FH domain-containing Bnr1p is a multifunctional protein interacting with a variety of cytoskeletal proteins in Saccharomyces cerevisiae

Abstract

Proteins containing formin homology domains, FH1 and FH2, are involved in cytokinesis or establishment of cell polarity in a variety of organisms. Bni1p and Bnr1p are FH proteins and potential targets of the Rho family small GTP-binding proteins in S. cerevisiae. We have shown that Bnr1p is localized at the bud neck to interact with Hof1p, involved in cytokinesis. We report here that the overexpression of BNR1 causes a cytokinesis de®ciency which is similar to the phenotypes of the septin mutants, including cdc3, cdc10, cdc11, and cdc12. The region required for the septin mutant phenotypes was mapped to Bnr1p (35 ± 500), which coincided with the region required for the bud-neck localization. To further isolate a gene interacting with BNI1 or BNR1, a multicopy suppressor of the bni1 bnr1 mutant was isolated. This gene encoded Smy1p, a kinesin-related protein. Bnr1p, but not Bni1p, directly interacted with the C-terminal region of Smy1p. The Smy1p-interacting region of Bnr1p was mapped to a region containing the FH2 domain. Bnr1p also directly interacted with Bud6p, a novel actin-binding protein. Bnr1p is thus a multifunctional protein which interacts with the septin system, a microtubule-dependent motor protein, and the actin system, to regulate cytoskeletal functions in S. cerevisiae.

Global Analysis of Cdc14 Phosphatase Reveals Diverse Roles in Mitotic Processes

“…Deletion of BNI1 causes a delay of or a failure to complete actomyosin ring contraction (64), and Bni1 may be particularly important for the incorporation of actin filaments into the actomyosin ring during mitosis (31). Overexpression of BNR1 causes a cytokinesis defect (65). Cdc14-dependent dephosphorylation of Bni1 and/or Bnr1 may alter the localization of these proteins, a step that might be necessary for timely ring contraction and cytokinesis.…”

Advances in Cytokinesis Research. Cytokinesis in Budding Yeast: The Relationship between Actomyosin Ring Function and Septum Formation.

“…There are two FH proteins in budding yeast: Bni1p and Bnr1p. Bni1p localizes to the presumptive bud site, the tip of a small bud, and the neck of a large-budded cell, whereas Bnr1p localizes to the bud neck throughout the cell cycle (Evangelista et al, 1997;Fujiwara et al, 1998;Kamei et al, 1998;Kikyo et al, 1999). Deletion of BNI1 or BNR1 alone is not lethal, but deletion of both causes cell lethality, suggesting that Bni1p and Bnr1p share at least one essential function (Kamei et al, 1998;Vallen et al, 2000).…”

Differential Activities and Regulation of Saccharomyces cerevisiae Formin Proteins Bni1 and Bnr1 by Bud6

“…We tested direct biochemical interactions of Bni1 and Bnr1 (immobilized on beads) with a purified soluble carboxyl-terminal fragment of Bud6 (C-Bud6; residues 489 -788) that we previously showed stimulates Bni1-induced actin assembly in vitro (6). This fragment encompasses the region of Bud6 that interacted with Bni1 and Bnr1 in two-hybrid assays (21,37). As shown in Fig.…”