The Schizosaccharomyces pombe cdc3+ gene encodes a profilin essential for cytokinesis.
The fission yeast Schizosaccharomyces pombe divides by medial fission and, like many higher eukaryotic cells, requires the function of an F-actin contractile ring for cytokinesis. In S. pombe, a class of cdc- mutants defective for cytokinesis, but not for DNA replication, mitosis, or septum synthesis, have been identified. In this paper, we present the characterization of one of these mutants, cdc3-124. Temperature shift experiments reveal that mutants in cdc3 are incapable of forming an F-actin contractile ring. We have molecularly cloned cdc3 and used the cdc3+ genomic DNA to create a strain carrying a cdc3 null mutation by homologous recombination in vivo. Cells bearing a cdc3-null allele are inviable. They arrest the cell cycle at cytokinesis without forming a contractile ring. DNA sequence analysis of the cdc3+ gene reveals that it encodes profilin, an actin-monomer-binding protein. In light of recent studies with profilins, we propose that Cdc3-profilin plays an essential role in cytokinesis by catalyzing the formation of the F-actin contractile ring. Consistent with this proposal are our observations that Cdc3-profilin localizes to the medial region of the cell where the F-actin contractile ring forms, and that it is essential for F-actin ring formation. Cells overproducing Cdc3-profilin become elongated, dumbbell shaped, and arrest at cytokinesis without any detectable F-actin staining. This effect of Cdc3-profilin overproduction is relieved by introduction of a multicopy plasmid carrying the actin encoding gene, act1+. We attribute these effects to potential sequestration of actin monomers by profilin, when present in excess.
Balasubramanian
M K
MK
Department of Cell Biology, Vanderbilt University, School of Medicine, Nashville, Tennessee 37232.
Hirani
B R
BR
Burke
J D
JD
Gould
K L
KL
D000199:Actins / Q000302:isolation & purification; D000595:Amino Acid Sequence; D001483:Base Sequence; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000235:genetics*; D002467:Cell Nucleus / Q000648:ultrastructure; D003001:Cloning, Molecular; D003285:Contractile Proteins; D005455:Fluorescent Antibody Technique; D005656:Fungal Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D005800:Genes, Fungal / Q000235:genetics*; D008840:Microfilament Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D009154:Mutation; D051304:Profilins; D011994:Recombinant Proteins / Q000096:biosynthesis; D012568:Schizosaccharomyces / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
D000199:Actins; D018797:Cell Cycle Proteins; D003285:Contractile Proteins; D005656:Fungal Proteins; D008840:Microfilament Proteins; D051304:Profilins; D011994:Recombinant Proteins; D029702:Schizosaccharomyces pombe Proteins; C490133:cdc3 protein, S pombe