BNI1/YNL271C Summary Help

Standard Name BNI1 1
Systematic Name YNL271C
Alias PPF3 2 , SHE5 3
Feature Type ORF, Verified
Description Formin; polarisome component; nucleates the formation of linear actin filaments, involved in cell processes such as budding and mitotic spindle orientation which require the formation of polarized actin cables, functionally redundant with BNR1 (4, 5, 6, 7, 8, 9 and see Summary Paragraph)
Name Description Bud Neck Involved 10
Chromosomal Location
ChrXIV:135383 to 129522 | ORF Map | GBrowse
Note: this feature is encoded on the Crick strand.
Gene Ontology Annotations All BNI1 GO evidence and references
  View Computational GO annotations for BNI1
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 3 genes
Classical genetics
Large-scale survey
588 total interaction(s) for 314 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 17
  • Affinity Capture-RNA: 3
  • Affinity Capture-Western: 5
  • Biochemical Activity: 7
  • Co-crystal Structure: 1
  • Co-localization: 1
  • Reconstituted Complex: 13
  • Two-hybrid: 35

Genetic Interactions
  • Dosage Lethality: 6
  • Dosage Rescue: 10
  • Negative Genetic: 70
  • Phenotypic Enhancement: 108
  • Phenotypic Suppression: 9
  • Positive Genetic: 5
  • Synthetic Growth Defect: 105
  • Synthetic Lethality: 188
  • Synthetic Rescue: 5

Expression Summary
Length (a.a.) 1,953
Molecular Weight (Da) 219,672
Isoelectric Point (pI) 6.49
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrXIV:135383 to 129522 | ORF Map | GBrowse
Note: this feature is encoded on the Crick strand.
Last Update Coordinates: 2011-02-03 | Sequence: 2011-02-03
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..5862 135383..129522 2011-02-03 2011-02-03
Retrieve sequences
Analyze Sequence
S288C only
S288C vs. other species
S288C vs. other strains
External Links All Associated Seq | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000005215

The S. cerevisiae genome encodes two genes that are members of the formin family, BNI1 and BNR1, which assemble linear actin cables in the bud and bud neck, respectively (11). Formins are a conserved family of proteins that promote the assembly of actin filaments, a function that is necessary for remodeling of the actin cytoskeleton during such processes as budding, mating, cytokinesis, endocytosis, and in higher cells, cell adhesion and migration. The hallmark of formin proteins is the presence of two highly conserved FH (formin homology) domains: the FH1 domain, containing polyproline motifs that mediate binding to profilin, which in turn binds actin monomers; and the FH2 domain, which nucleates actin assembly (reviewed in 12 and 13). Bni1p and Bnr1p are classified in the diaphanous-related formin (DRF) group of metazoan formins, named for the founding Drosophila gene diaphanous (dia) (14). The FH2 domains of Bni1p and Bnr1p are distinct from those of the metazoan groups, containing a yeast-specific insert that is not found in other organisms (15). In addition to FH1 and FH2 domains, DRFs also contain a regulatory Rho-binding domain (RBD) and a Dia-autoregulatory-domain (DAD) (reviewed in 13). Null mutations in either BNI1 or BNR1 do not impair cell viability, but the double bni1 bnr1 mutant is inviable, indicating that formins play an essential role in S. cerevisiae (16).

A model for formin-mediated actin assembly proposes the following sequence of events (reviewed in 17). Activated Rho protein binds to the formin RBD and releases the formin from a conformation in which it is autoinhibited, due to interaction between its amino and carboxy termini, to a conformation that exposes the FH1 and FH2 domains. The FH1 domain interacts with profilin-bound actin monomers, "delivering" them to the FH2 domain, which is dimeric in structure and thus may interact with two actin monomers to stabilize a dimeric actin form, prior to polymerization to form actin cables. The FH2 domain remains associated with the growing end of the filament to protect it from interaction with capping proteins (an FH2 function termed "processive capping").

Consistent with the model, Bni1p is known to be a downstream target of the small GTPase Rho1p, which regulates reorganization of the actin cytoskeleton, and hence the process of bud formation (1, 18). In addition, Bni1p activation is regulated by Rho3p and Rho4p, which affect the inhibitory interaction between the RBD and the DAD domains in the formin, and the Rho protein Cdc42p is needed for proper cable assembly during initiation of bud growth (8). Bni1p autoinhibition is also disrupted by the action of Prk1p kinase, which phosphorylates Bni1p (19). Support for the model also comes from crystal structure studies of the Bni1p FH2 domain complexed with actin (20).

Bni1p functions as a component of the polarisome, a complex that also includes Spa2p, Bud6p, Pea2p, Msb3p, and Msb4p (21, 22, reviewed in 23). The polarisome is important for determining cell polarity; it acts as the focal point for polymerization of actin monomers into actin cables, and is required for the proper initiation of bud growth and the proper shape of vegetative buds and mating shmoos (reviewed in 23, 24).

Localization of Bni1p is dynamic; in small-budded cells Bni1p moves along the bud cortex, becoming more abundant at the bud tip and bud neck as growth proceeds (25, 26). In addition, Bni1p is found as abundant cytoplasmic speckles throughout the cell cycle; these speckles are associated with actin cables and are not visible upon loss of polymerized actin (26).

Although bni1 null mutants are viable, they exhibit a shorter replicative lifespan than wild type cells (27). They are partially deficient in cytokinesis, and homozygous diploids are predominantly round in shape, exhibit a random budding pattern, and are defective for filamentous growth in nitrogen starvation conditions (28, reviewed in 10). Null mutants also display reduced mating efficiencies in response to pheromone treatment, and detailed genetic studies indicate Bni1p plays a role in polarized recruitment of Ste5p and the consequent activation of Fus3p during mating response (29).

Last updated: 2010-04-23 Contact SGD

References cited on this page View Complete Literature Guide for BNI1
1) Kohno H, et al.  (1996) Bni1p implicated in cytoskeletal control is a putative target of Rho1p small GTP binding protein in Saccharomyces cerevisiae. EMBO J 15(22):6060-8
2) Yorihuzi T and Ohsumi Y  (1994) Saccharomyces cerevisiae MATa mutant cells defective in pointed projection formation in response to alpha-factor at high concentrations. Yeast 10(5):579-94
3) Jansen RP, et al.  (1996) Mother cell-specific HO expression in budding yeast depends on the unconventional myosin myo4p and other cytoplasmic proteins. Cell 84(5):687-97
4) Chang F and Peter M  (2002) Cell biology. Formins set the record straight. Science 297(5581):531-2
5) Pruyne D, et al.  (2002) Role of formins in actin assembly: nucleation and barbed-end association. Science 297(5581):612-5
6) Sagot I, et al.  (2002) An actin nucleation mechanism mediated by Bni1 and profilin. Nat Cell Biol 4(8):626-31
7) Lew DJ  (2002) Formin' actin filament bundles. Nat Cell Biol 4(2):E29-30
8) Dong Y, et al.  (2003) Formin-dependent actin assembly is regulated by distinct modes of Rho signaling in yeast. J Cell Biol 161(6):1081-92
9) Moore TI, et al.  (2013) Yeast G-proteins mediate directional sensing and polarization behaviors in response to changes in pheromone gradient direction. Mol Biol Cell 24(4):521-34
10) Zahner JE, et al.  (1996) Genetic analysis of the bipolar pattern of bud site selection in the yeast Saccharomyces cerevisiae. Mol Cell Biol 16(4):1857-70
11) Pruyne D, et al.  (2004) Stable and dynamic axes of polarity use distinct formin isoforms in budding yeast. Mol Biol Cell 15(11):4971-89
12) Goode BL and Eck MJ  (2007) Mechanism and function of formins in the control of actin assembly. Annu Rev Biochem 76():593-627
13) Evangelista M, et al.  (2003) Formins: signaling effectors for assembly and polarization of actin filaments. J Cell Sci 116(Pt 13):2603-11
14) Castrillon DH and Wasserman SA  (1994) Diaphanous is required for cytokinesis in Drosophila and shares domains of similarity with the products of the limb deformity gene. Development 120(12):3367-77
15) Higgs HN and Peterson KJ  (2005) Phylogenetic analysis of the formin homology 2 domain. Mol Biol Cell 16(1):1-13
16) Vallen EA, et al.  (2000) Roles of Hof1p, Bni1p, Bnr1p, and myo1p in cytokinesis in Saccharomyces cerevisiae. Mol Biol Cell 11(2):593-611
17) Moseley JB, et al.  (2006) Formin proteins: purification and measurement of effects on actin assembly. Methods Enzymol 406():215-34
18) Tolliday N, et al.  (2002) Rho1 directs formin-mediated actin ring assembly during budding yeast cytokinesis. Curr Biol 12(21):1864-70
19) Wang J, et al.  (2009) Regulation of the yeast formin Bni1p by the actin-regulating kinase Prk1p. Traffic 10(5):528-35
20) Otomo T, et al.  (2005) Structural basis of actin filament nucleation and processive capping by a formin homology 2 domain. Nature 433(7025):488-94
21) Sheu YJ, et al.  (1998) Spa2p interacts with cell polarity proteins and signaling components involved in yeast cell morphogenesis. Mol Cell Biol 18(7):4053-69
22) Tcheperegine SE, et al.  (2005) Regulation of cell polarity by interactions of Msb3 and Msb4 with Cdc42 and polarisome components. Mol Cell Biol 25(19):8567-80
23) Pruyne D and Bretscher A  (2000) Polarization of cell growth in yeast. I. Establishment and maintenance of polarity states. J Cell Sci 113 ( Pt 3):365-75
24) Guarente L  (2010) Forever young. Cell 140(2):176-8
25) Ozaki-Kuroda K, et al.  (2001) Dynamic localization and function of Bni1p at the sites of directed growth in Saccharomyces cerevisiae. Mol Cell Biol 21(3):827-39
26) Buttery SM, et al.  (2007) Yeast Formins Bni1 and Bnr1 Utilize Different Modes of Cortical Interaction during the Assembly of Actin Cables. Mol Biol Cell 18(5):1826-38
27) Liu B, et al.  (2010) The Polarisome Is Required for Segregation and Retrograde Transport of Protein Aggregates. Cell 140(2):257-267
28) Mosch HU and Fink GR  (1997) Dissection of filamentous growth by transposon mutagenesis in Saccharomyces cerevisiae. Genetics 145(3):671-84
29) Qi M and Elion EA  (2005) Formin-induced actin cables are required for polarized recruitment of the Ste5 scaffold and high level activation of MAPK Fus3. J Cell Sci 118(Pt 13):2837-48