An IQGAP-related protein controls actin-ring formation and cytokinesis in yeast

Curr Biol. 1997 Dec 1;7(12):921-9. doi: 10.1016/s0960-9822(06)00411-8.


Background: Proteins of the IQGAP family have been identified as candidate effectors for the Rho family of GTPases; however, little is known about their cellular functions. The domain structures of IQGAP family members make them excellent candidates as regulators of the cytoskeleton: their sequences include an actin-binding domain homologous to that found in calponin, IQ motifs for interaction with calmodulin, and a GTPase-binding domain.

Results: The genomic sequence of Saccharomyces cerevisiae revealed a single gene encoding an IQGAP family member (denoted IQGAP-related protein: Iqg1). Iqg1 and IQGAPs share similarity along their entire length, with an amino-terminal calponin-homology (CH) domain, IQ repeats, and a conserved carboxyl terminus. In contrast to IQGAPs, Iqg1 lacks an identifiable GAP motif, a WW domain, and IR repeats, although the functions of these domains in IQGAPs are not well defined. Deletion of the IQG1 gene resulted in lethality. Cellular defects included a deficiency in cytokinesis, altered actin organization, aberrant nuclear segregation, and cell lysis. The primary defect appeared to be a cytokinesis defect, and the other problems possibly arose as a consequence of this initial defect. Consistent with a role in cytokinesis, Iqg1 co-localizes with an actin ring encircling the mother-bud neck late in the cell cycle -a putative cytokinetic ring. IQG1 overexpression resulted in premature actin-ring formation, suggesting that Iqg1 activity temporally controls formation of this structure during the cell cycle.

Conclusions: Yeast IQGAP-related protein, Iqg1, is an important regulator of cellular morphogenesis, inducing actin-ring formation in association with cytokinesis.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actin Cytoskeleton / metabolism
  • Actins / metabolism*
  • Amino Acid Sequence
  • Cell Division / physiology*
  • Fungal Proteins / genetics
  • Fungal Proteins / physiology*
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism
  • GTPase-Activating Proteins
  • Gene Expression
  • Molecular Sequence Data
  • Proteins / chemistry*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / growth & development
  • Saccharomyces cerevisiae / physiology*
  • Sequence Homology, Amino Acid


  • Actins
  • Fungal Proteins
  • GTPase-Activating Proteins
  • Proteins
  • GTP Phosphohydrolases