Identification and characterization of Schizosaccharomyces pombe asp1(+) agene that interacts with mutations in the Arp2/3 complex and actin

The Arp2/3 complex is an essential component of the actin cytoskeleton in y east and is required for the movement of actin patches. In an attempt to id entify proteins that interact with this complex in the fission yeast Schizo saccharomyces pombe, we sought high-copy suppressors of the S. pombe arp3-c 1 mutant, and have identified one, which we have termed asp1(+). The asp1() open reading frame (ORF) predicts a highly conserved protein of 921 amino acids with a molecular mass of 106 kD that does not contain motifs of know n function. Neither asp1(+) nor its apparent Saccharomyces cerevisiae ortho log, VIP1, are essential genes. However, disruption of asp1(+) leads to alt ered morphology and growth properties at elevated temperatures and defects in polarized growth. The asp1 disruption strain also is hyper-sensitive to Caf ions and to low pH conditions. Although Asp1p is not stably associated with the Arp2/3 complex nor localized in any discrete structure within the cytoplasm, the asp1 disruption mutant was synthetically lethal with mutatio ns in components of the Arp2/3 complex, arp3-c1 and sop2-1, as well as with a mutation in actin, act1-48. Moreover, the vip1 disruption strain showed a negative genetic interaction with a las17 Delta strain. We conclude that Asp1p/Vip1p is important for the function of die cortical actin cytoskeleto n.