Interaction of Bnr1p with a Novel Src Homology 3 Domain-containing Hof1p

Proteins containing the formin homology (FH) domains FH1 and FH2 are involved in cytokinesis or establishment of cell polarity in a variety of organisms. We have shown that the FH proteins Bni1p and Bnr1p are potential targets of the Rho family small GTP-binding proteins and bind to an actin-binding protein, profilin, at their proline-rich FH1 domains to regulate reorganization of the actin cytoskeleton in the yeast Saccharomyces cerevisiae. We found here that a novel Src homology 3 (SH3) domain-containing protein, encoded by YMR032w, interacted with Bnr1p in a GTP-Rho4p-dependent manner through the FH1 domain of Bnr1p and the SH3 domain of Ymr032wp. Ymr032wp weakly bound to Bni1p. Ymr032wp was homologous to cdc15p, which is involved in cytokinesis in Schizosaccharomyces pombe, and we named this geneHOF1 (homolog of cdc 15). Both Bnr1p and Hof1p were localized at the bud neck, and both the bnr1 and hof1 mutations showed synthetic lethal interactions with the bni1 mutation. The hof1 mutant cells showed phenotypes similar to those of the septin mutants, indicating thatHOF1 is involved in cytokinesis. These results indicate that Bnr1p directly interacts with Hof1p as well as with profilin to regulate cytoskeletal functions in S. cerevisiae. Proteins containing the formin homology (FH) domains FH1 and FH2 are involved in cytokinesis or establishment of cell polarity in a variety of organisms. We have shown that the FH proteins Bni1p and Bnr1p are potential targets of the Rho family small GTP-binding proteins and bind to an actin-binding protein, profilin, at their proline-rich FH1 domains to regulate reorganization of the actin cytoskeleton in the yeast Saccharomyces cerevisiae. We found here that a novel Src homology 3 (SH3) domain-containing protein, encoded by YMR032w, interacted with Bnr1p in a GTP-Rho4p-dependent manner through the FH1 domain of Bnr1p and the SH3 domain of Ymr032wp. Ymr032wp weakly bound to Bni1p. Ymr032wp was homologous to cdc15p, which is involved in cytokinesis in Schizosaccharomyces pombe, and we named this geneHOF1 (homolog of cdc 15). Both Bnr1p and Hof1p were localized at the bud neck, and both the bnr1 and hof1 mutations showed synthetic lethal interactions with the bni1 mutation. The hof1 mutant cells showed phenotypes similar to those of the septin mutants, indicating thatHOF1 is involved in cytokinesis. These results indicate that Bnr1p directly interacts with Hof1p as well as with profilin to regulate cytoskeletal functions in S. cerevisiae. formin homology Src homology 3 DNA-binding domain of LexA transcriptional activation domain of GAL4 maltose-binding protein glutathione S-transferase kilobase pair(s). The Rho family belongs to the small G protein superfamily and regulates various cell functions through reorganization of the actin cytoskeleton (for reviews, see Refs. 1Hall A. Annu. Rev. Cell Biol. 1994; 10: 31-54Crossref PubMed Scopus (768) Google Scholar and 2Takai Y. Sasaki T. Tanaka K. Nakanishi H. Trends Biochem. Sci. 1995; 20: 227-231Abstract Full Text PDF PubMed Scopus (366) Google Scholar). Many potential targets of Rho have been identified (for a review, see Ref. 3Hall A. Science. 1998; 279: 509-514Crossref PubMed Scopus (5220) Google Scholar), but it has not yet been thoroughly clarified how Rho regulates reorganization of the actin cytoskeleton through these targets. The actin cytoskeleton plays a pivotal role in the budding processes in the yeast Saccharomyces cerevisiae (for a review, see Ref.4Cid V.J. Duran A. del-Rey F. Snyder M.P. Nombela C. Sanchez M. Microbiol. Rev. 1995; 59: 345-386Crossref PubMed Google Scholar). This yeast has the Rho family members, including RHO1, RHO2, RHO3, RHO4, and CDC42, which are involved in the budding processes (for reviews, see Refs. 4Cid V.J. Duran A. del-Rey F. Snyder M.P. Nombela C. Sanchez M. Microbiol. Rev. 1995; 59: 345-386Crossref PubMed Google Scholar and 5Tanaka K. Takai Y. Curr. Opin. Cell Biol. 1998; 10: 112-116Crossref PubMed Scopus (56) Google Scholar). We have isolatedBNI1 as a potential target of RHO1, which linksRHO1 with the actin cytoskeleton (6Kohno H. Tanaka K. Mino A. Umikawa M. Imamura H. Fujiwara T. Fujita Y. Hotta K. Qadota H. Watanabe T. Ohya Y. Takai Y. EMBO J. 1996; 15: 6060-6068Crossref PubMed Scopus (241) Google Scholar). BNI1 has subsequently been shown to be a potential target of CDC42, RHO3, and RHO4 (7Evangelista M. Blundell K. Longtine M.S. Chow C.J. Adames N. Pringle J.R. Peter M. Boone C. Science. 1997; 276: 118-122Crossref PubMed Scopus (530) Google Scholar). BNR1 is aBNI1-related gene and is a potential target of RHO4 (8Imamura H. Tanaka K. Hihara T. Umikawa M. Kamei T. Takahashi K. Sasaki T. Takai Y. EMBO J. 1997; 16: 2745-2755Crossref PubMed Scopus (271) Google Scholar). Bni1p and Bnr1p are members of the FH1 family of proteins, which are defined by the presence of two formin homology domains, the proline-rich FH1 domain and the FH2 domain. The FH proteins play an important role in the actin cytoskeleton-dependent processes, including cytokinesis and establishment of cell polarity (for reviews, see Refs. 9Frazier J.A. Field C.M. Curr. Biol. 1997; 7: R414-R417Abstract Full Text Full Text PDF PubMed Google Scholar and 10Wasserman S. Trends Cell Biol. 1998; 8: 111-115Abstract Full Text PDF PubMed Scopus (163) Google Scholar). We have recently shown that Bni1p interacts with elongation factor 1α, which binds to and bundles actin filaments (11Umikawa M. Tanaka K. Kamei T. Shimizu K. Imamura H. Sasaki T. Takai Y. Oncogene. 1998; 16: 2011-2016Crossref PubMed Scopus (62) Google Scholar), and that Spa2p is required for the localization of Bni1p at the bud tip (12Fujiwara T. Tanaka K. Mino A. Kikyo M. Takahashi K. Shimizu K. Takai Y. Mol. Biol. Cell. 1998; 9: 1221-1233Crossref PubMed Scopus (143) Google Scholar). Bni1p and Bnr1p, at their FH1 domains, bind to an actin monomer-binding protein, profilin, which is implicated in actin polymerization (7Evangelista M. Blundell K. Longtine M.S. Chow C.J. Adames N. Pringle J.R. Peter M. Boone C. Science. 1997; 276: 118-122Crossref PubMed Scopus (530) Google Scholar, 8Imamura H. Tanaka K. Hihara T. Umikawa M. Kamei T. Takahashi K. Sasaki T. Takai Y. EMBO J. 1997; 16: 2745-2755Crossref PubMed Scopus (271) Google Scholar). A proline-rich sequence also interacts with an SH3 domain, which is found in a wide variety of proteins, ranging from cytoskeletal components to signal transducing enzymes (for a review, see Ref. 13Musacchio A. Wilmanns M. Saraste M. Prog. Biophys. Mol. Biol. 1994; 61: 283-297Crossref PubMed Scopus (144) Google Scholar). Actually, the FH1 domain of mouse formin binds to SH3 domain-containing proteins (14Chan D.C. Bedford M.T. Leder P. EMBO J. 1996; 15: 1045-1054Crossref PubMed Scopus (194) Google Scholar), although its physiological significance remains obscure. We show here that a novel SH3 domain-containing protein, Hof1p, directly binds to the FH1 domain of Bnr1p through the SH3 domain in a GTP-Rho4p-dependent manner. The hof1 mutant shows a deficiency in cytokinesis. Both Hof1p and Bnr1p are localized at the bud neck, and both the hof1 and bnr1mutations show synthetic lethal interactions with the bni1mutation. Our results suggest that Bnr1p interacts with both Hof1p and profilin at its FH1 domain to regulate reorganization of the actin cytoskeleton. Wild type yeast strains OHNY1 (MATa ura3 leu2 trp1 his3 ade2) and OHNY3 (MATa/MATα ura3/ura3 leu2/leu2 trp1/trp1 his3/his3 ade2/ade2) (15Ozaki K. Tanaka K. Imamura H. Hihara T. Kameyama T. Nonaka H. Hirano H. Matsuura Y. Takai Y. EMBO J. 1996; 15: 2196-2207Crossref PubMed Scopus (184) Google Scholar) were used for cytological and genetic studies. TAT7 (MATa trp1 leu2 his3 LYS2::lexA-HIS3 ura3::lexA-lacZ) was used for the two-hybrid studies. Yeast strains were usually grown in rich medium (yeast extract peptone dextrose adenine uracil, YPDAU), and yeast transformants were selected in dextrose-containing (synthetic dextrose) or galactose-containing (synthetic galactose) selection media (12Fujiwara T. Tanaka K. Mino A. Kikyo M. Takahashi K. Shimizu K. Takai Y. Mol. Biol. Cell. 1998; 9: 1221-1233Crossref PubMed Scopus (143) Google Scholar). Yeast transformations were performed by the lithium acetate methods (16Gietz D. Jean A.S. Woods R.A. Schiestl R.H. Nucleic Acids Res. 1992; 20: 1425Crossref PubMed Scopus (2895) Google Scholar). Standard yeast genetic manipulations were performed as described (17Sherman F. Fink G.R. Hicks J.B. Methods in Yeast Genetics. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY1986Google Scholar). An Escherichia coli strain DH5α was used for construction and propagation of plasmids and purification of recombinant proteins. Standard molecular biological techniques were used for construction of plasmids, DNA sequencing, and polymerase chain reaction (18Sambrook J. Fritsch E.F. Maniatis T. Molecular Cloning: A Laboratory Manual. 2nd Ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY1989Google Scholar). Two-hybrid plasmids were constructed by inserting various truncated fragments of BNR1 or BNI1 and HOF1, generated by polymerase chain reaction or digestion with restriction enzymes, into pBTM116-HA (8Imamura H. Tanaka K. Hihara T. Umikawa M. Kamei T. Takahashi K. Sasaki T. Takai Y. EMBO J. 1997; 16: 2745-2755Crossref PubMed Scopus (271) Google Scholar), encoding DBDLexA, and pACTII-HK (15Ozaki K. Tanaka K. Imamura H. Hihara T. Kameyama T. Nonaka H. Hirano H. Matsuura Y. Takai Y. EMBO J. 1996; 15: 2196-2207Crossref PubMed Scopus (184) Google Scholar), encoding ADGAL4, respectively. pKT10-RHO4ΔC, pKT10-RHO4ΔC(Q70L), pKT10-RHO4ΔC(T25N), pKT10-RHO3ΔC, and pKT10-RHO3ΔC(Q74L) were constructed by placing the BamHI (filled in)-SmaI fragments of RHO4ΔC, RHO4ΔC(Q70L), RHO4ΔC-(T25N), RHO3ΔC, and RHO3ΔC(Q74L) (8Imamura H. Tanaka K. Hihara T. Umikawa M. Kamei T. Takahashi K. Sasaki T. Takai Y. EMBO J. 1997; 16: 2745-2755Crossref PubMed Scopus (271) Google Scholar), respectively, downstream of the TDH3 promoter of pKT10 expression vector (19Tanaka K. Nakafuku M. Tamanoi F. Kaziro Y. Matsumoto K. Toh-e A. Mol. Cell. Biol. 1990; 10: 4303-4313Crossref PubMed Scopus (241) Google Scholar). pMAL-c2-HOF1(551–669) was made by inserting the 0.4-kbp EcoRI-SalI fragment of HOF1, corresponding to amino acid positions from 551 to 669 of Hof1p, into the EcoRI-SalI site of pMAL-c2 (New England Biolabs, Inc., Beverly, MA). pGEX-4T-2-BNR1(757–1326) was made by inserting the 1.7-kbp BamHI-BamHI fragment of BNR1 into the BamHI site of pGEX-4T-2 (Amersham Pharmacia Biotech). pUC19-HOF1 was made by inserting the 2.0-kbp BamHI-SmaI fragment of HOF1, containing the HOF1 open reading frame, from pACTII-HK-HOF1 into the BamHI-SmaI site of pUC19. The disruption plasmid for HOF1, pUC19-hof1::LEU2, was made by inserting the 2.2-kbp LEU2 fragment into the XhoI site of pUC19-HOF1, corresponding to amino acid position 86 of Hof1p. pKO11 is a pRS316-based (20Sikorski R.S. Hieter P. Genetics. 1989; 122: 19-27Crossref PubMed Google Scholar) expression vector that contains theGAL1 promoter, the two HA epitopes-encoding region just downstream of the initiation codon, a multicloning site, and theTDH3 terminator. pKO11-BNR1 was made by inserting the 4.1-kbp SmaI-SmaI fragment from pACTII-HK-BNR1(1–1374) (8Imamura H. Tanaka K. Hihara T. Umikawa M. Kamei T. Takahashi K. Sasaki T. Takai Y. EMBO J. 1997; 16: 2745-2755Crossref PubMed Scopus (271) Google Scholar) into the SmaI site of pKO11. pKO11-HOF1 was made by inserting the 2.0-kbpBamHI-SmaI fragment from pACTII-HK-HOF1 into theBamHI-SmaI site of pKO11. A plasmid containing a gene fused to DBDLexA was transformed into TAT7, and the resultant transformant was retransformed by a plasmid containing a gene fused to ADGAL4. Cells of each transformant were cultured in synthetic dextrose medium lacking tryptophan and leucine, and β-galactosidase activity was measured quantitatively according to theO-nitrophenyl-β-d-galactopyranoside assay method (21Guarente L. Methods Enzymol. 1983; 101: 181-191Crossref PubMed Scopus (873) Google Scholar). The values (Miller units) are the averages of β-galactosidase activity for three transformants, and each measured value was within 50% of the average. For qualitative assay for β-galactosidase activity, cells of each transformant were placed on the nitrocellulose filter and stained with 5-bromo-4-chloro-3-indolyl β-d-galactopyranoside (22Vojtek A.B. Hollenberg S.M. Cooper J.A. Cell. 1993; 74: 205-214Abstract Full Text PDF PubMed Scopus (1663) Google Scholar). pUC19-hof1::LEU2 was cut withBamHI and SmaI, and the digested DNA was introduced into OHNY3. The genomic DNA was isolated from each transformant, and the proper disruption of HOF1 was verified by polymerase chain reaction (data not shown). A transformant in which one HOF1 allele was disrupted was subjected to tetrad analysis. All dissected asci (11 asci) showed a 2 Leu−:2 Leu+ segregation pattern, and all of the Leu+clones showed the temperature-sensitive growth phenotype. One Leu+ strain, TKUK1, was used as a hof1 mutant in this study. Cdc11p and HA-tagged proteins were stained with the anti-Cdc11p antibody (kindly provided by J. Pringle) and the anti-HA monoclonal antibody, 12CA5, respectively (23Yamochi W. Tanaka K. Nonaka H. Maeda A. Musha T. Takai Y. J. Cell Biol. 1994; 125: 1077-1093Crossref PubMed Scopus (209) Google Scholar). Actin and DNA were stained with rhodamine-phalloidin (Molecular Probes, Inc., Eugene, OR) and 4′,6′-diamidino-2-phenylindole dihydrochloride (Sigma), respectively (23Yamochi W. Tanaka K. Nonaka H. Maeda A. Musha T. Takai Y. J. Cell Biol. 1994; 125: 1077-1093Crossref PubMed Scopus (209) Google Scholar). Chitin was stained with Calcofluor White M2R New (Sigma) (24Pringle J.R. Methods Enzymol. 1991; 194: 732-735Crossref PubMed Scopus (223) Google Scholar). Stained cells were observed with a Zeiss Axiophoto microscope (Carl Zeiss, Oberkochen, Germany) and photographed with a peltier cooling 3CCD color camera (C5810–01; Hamamatsu Photonics KK, Hamamatsu, Japan). Recombinant MBP-Hof1p(551–669) was purified from DH5α carrying pMAL-c2-HOF1(551–669) using an amylose resin column (New England Biolabs, Inc.) (25Guan C.L.P. Riggs P.D Inouye H. Gene. 1988; 67: 21-30Crossref PubMed Scopus (546) Google Scholar). Recombinant GST-Bnr1p(757–1326) was purified from DH5α carrying pGEX-4T-2-BNR1(757–1326) using a glutathione-Sepharose 4B column (Amersham Pharmacia Biotech) (26Kikuchi A. Kuroda S. Sasaki T. Kotani K. Hirata K. Katayama M. Takai Y. J. Biol. Chem. 1992; 267: 14611-14615Abstract Full Text PDF PubMed Google Scholar). Purified MBP-Hof1p(551–669) or MBP (4 nmol each) in 600 μl of Buffer A (20 mm Tris-HCl (pH 7.5), 1 mmEDTA, and 1 mm dithiothreitol) was loaded onto a glutathione-Sepharose 4B column that was prebound to GST-Bnr1p(757–1326) (400 pmol) or GST (4 nmol). Each column was washed with 20 column volumes of Buffer A. GST-Bnr1p(757–1326) or GST was eluted with 300 μl of Buffer A containing 10 mm reduced glutathione. An aliquot (30 μl) of each eluate was subjected to SDS-polyacrylamide gel electrophoresis, followed by protein staining with Coomassie Brilliant Blue. SDS-polyacrylamide gel electrophoresis and determination of protein concentrations were performed as described (27Laemmli U.K. Nature. 1970; 227: 680-685Crossref PubMed Scopus (207231) Google Scholar, 28Bradford M.M. Anal. Biochem. 1976; 72: 248-254Crossref PubMed Scopus (216440) Google Scholar). We examined by the two-hybrid method whether Bnr1p(757–1374) and Bni1p(1239–1953), containing the FH1 and FH2 domains, interacted with an SH3 domain-containing protein. Among four proteins containing an SH3 domain tested, including Abp1p, Sla1p, Rvs167p, and Ymr032wp, only Ymr032wp bound to both Bnr1p and Bni1p (data not shown). Deletion analysis of Bnr1p indicated that Bnr1p bound to Ymr032wp at its FH1 domain, although full-length Bnr1p did not bind to Ymr032wp (Fig. 1 A). In contrast, Bni1p(1239–1953), containing the FH1, FH2, and its C-terminal domains, weakly bound to Hof1p, but neither the FH1 domain itself nor full-length Bni1p did (Fig. 1 B). analysis indicated that the of expression of were similar to those of (data not shown). Deletion analysis of Ymr032wp indicated that Ymr032wp bound to Bnr1p at its SH3 domain (Fig. 1 Ymr032wp is homologous to cdc15p, which is involved in cytokinesis in Schizosaccharomyces C. A. L. S. K. Cell. 1995; Full Text PDF PubMed Scopus Google Scholar). Both of the proteins have a region at the with potential to a C-terminal SH3 domain, and a which is implicated in of proteins M. Cell Biol. 1990; Google Scholar). We named Ymr032wp Hof1p (homolog of cdc 15). whether Hof1p directly interacts with Bnr1p, containing the SH3 domain, and containing the FH1 domain, were fused to MBP and respectively, and these proteins were in coli and MBP-Hof1p(551–669) bound to GST-Bnr1p(757–1326) at a of but it did not bind to GST (Fig. MBP did not bind to This that Hof1p directly interacts with We examined by the two-hybrid method whether full-length Bnr1p interacted with Hof1p in a manner. Wild type or mutant carrying an amino acid that in the F. Nature. 1991; PubMed Scopus Google Scholar) or the or Mol. Cell. Biol. 1991; PubMed Scopus (184) Google Scholar) was in the two-hybrid strain, TAT7, full-length Bnr1p and full-length Hof1p. These did not the C-terminal site to of with the (8Imamura H. Tanaka K. Hihara T. Umikawa M. Kamei T. Takahashi K. Sasaki T. Takai Y. EMBO J. 1997; 16: 2745-2755Crossref PubMed Scopus (271) Google Scholar). Hof1p interacted with full-length Bnr1p but not type or was (Fig. 3 A). We examined whether full-length Bni1p interacted with Hof1p in a Rho manner. Hof1p did not with full-length Bni1p or was (Fig. 3 B). analysis indicated that type and mutant and type and mutant were at a similar (data not shown). We not the of or on the of these proteins cell growth with the C-terminal K. T. M. H. M. K. and Y. These results indicate that full-length Bnr1p interacts with Hof1p in a GTP-Rho4p-dependent manner but that full-length Bni1p not with Hof1p, of the presence or the of the The HOF1 gene was disrupted with The hof1 mutant showed the temperature-sensitive growth (data not shown). The cells of the hof1 mutant were observed a microscope and of the hof1 mutant cells a and bud (Fig. of DNA and that these hof1 mutant cells showed and the of the cells (Fig. A). of actin that the cells actin at the bud tip but not at the (Fig. B). These phenotypes are similar to those of the septin Pringle J.R. J. Cell Biol. PubMed Scopus Google Scholar). The septin family members, including and are involved in cytokinesis (for reviews, see Field C.M. Curr. Biol. 1994; Full Text Full Text PDF PubMed Scopus Google Scholar and M.S. H. C. Pringle J.R. Curr. Opin. Cell Biol. 1996; 8: PubMed Scopus Google Scholar). Our results indicate that the hof1 mutant is in cytokinesis. The physiological significance of the of Bnr1p with Hof1p was examined We have shown that the is lethal with the bni1 (8Imamura H. Tanaka K. Hihara T. Umikawa M. Kamei T. Takahashi K. Sasaki T. Takai Y. EMBO J. 1997; 16: 2745-2755Crossref PubMed Scopus (271) Google Scholar). The hof1 mutant was with the bni1 and the hof1 was also lethal with (data not shown). In contrast, was not lethal with (data not shown). These results suggest thatHOF1 and BNR1 in a similar The localization of Hof1p was examined by the analysis. gene was the of a staining was not observed (data not shown). was the of the promoter on a The expression of the temperature-sensitive growth of the hof1 mutant (data not indicating that the of the HA not the functions of was localized at the bud in both and as was Cdc11p (Fig. of was and was also localized at the bud (Fig. We have here the interactions of Bnr1p with four SH3 domain-containing proteins, Hof1p, Abp1p, Sla1p, and Rvs167p, and shown that Bnr1p interacts with only Hof1p. Abp1p, Sla1p, and are with actin or actin (for a review, see Ref. 4Cid V.J. Duran A. del-Rey F. Snyder M.P. Nombela C. Sanchez M. Microbiol. Rev. 1995; 59: 345-386Crossref PubMed Google Scholar), Bnr1p and Hof1p are at the bud through the cell that Bnr1p interacts with Hof1p SH3 domain-containing proteins. We have shown that this of Bnr1p with Hof1p is and an activity of its protein H. Sasaki T. Takai Y. T. Nature. 1998; PubMed Scopus Google Scholar). This with the results that although the FH1 domain of Bnr1p interacts with Hof1p in the of full-length Bnr1p interacts with it only in a GTP-Rho4p-dependent that the of Rho family to each target its as described for the (for a review, see Ref. Curr. Opin. Cell Biol. 1997; 9: PubMed Scopus Google Scholar). We have shown that Hof1p also interacts with but this is The FH1 domain of Bni1p was not for the with Hof1p, and full-length Bni1p did not with Hof1p in a manner. Bni1p is localized at the bud tip (12Fujiwara T. Tanaka K. Mino A. Kikyo M. Takahashi K. Shimizu K. Takai Y. Mol. Biol. Cell. 1998; 9: 1221-1233Crossref PubMed Scopus (143) Google Scholar). the physiological significance of the remains obscure. The FH1 domain of contains four proline-rich and The SH3 domain of Hof1p interacted with a region of Bnr1p containing the two but not that containing the two in the two-hybrid although the was (data not shown). The FH1 domain of also interacted with profilin in the two-hybrid method (data not shown). These results indicate that the FH1 domain of Bnr1p binds to both Hof1p and profilin and are with an that both the SH3 domain and profilin a similar which of an of (for a review, see Ref. Curr. Biol. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). In contrast, the FH1 domain of Bni1p contains four proline-rich and but the two proline-rich not a at the position from the The of the FH1 domain of Bni1p to with Hof1p be to this In S. pombe, C. A. L. S. K. Cell. 1995; Full Text PDF PubMed Scopus Google Scholar), J. Cell Biol. 1994; 125: PubMed Scopus Google Scholar), and FH F. D. P. J. Cell Biol. 1997; PubMed Scopus Google Scholar) are involved in cytokinesis. has not yet been shown that interacts with but interacts with F. D. P. J. Cell Biol. 1997; PubMed Scopus Google Scholar). of an FH protein with both profilin and an SH3 domain-containing protein be a in the of of FH proteins. We have shown that the disruption mutant of HOF1 is in cytokinesis. This is with the is also involved in cytokinesis in S. C. A. L. S. K. Cell. 1995; Full Text PDF PubMed Scopus Google Scholar) and that Hof1p is localized at the bud neck, as is a Hof1p homologous the SH3 domain, with and proteins in and mouse C. A. L. S. K. Cell. 1995; Full Text PDF PubMed Scopus Google Scholar). These proteins be involved in cytokinesis. A protein to has recently been implicated in cytokinesis in S. cerevisiae J.A. J. Curr. Biol. 1997; 7: Full Text Full Text PDF PubMed Scopus Google Scholar, J. J. Cell Biol. 1998; PubMed Scopus Google Scholar). is localized at the bud and with actin be to whether Hof1p or interacts with We Pringle of for the anti-Cdc11p