Fission Yeast Pob1p, Which Is Homologous to Budding Yeast Boi Proteins and Exhibits Subcellular Localization Close to Actin Patches, Is Essential for Cell Elongation and Separation

Abstract

The fission yeast pob1 gene encodes a protein of 871 amino acids carrying an SH3 domain, a SAM domain, and a PH domain. Gene disruption and construction of a temperature-sensitive pob1 mutant indicated that pob1 is essential for cell growth. Loss of its function leads to quick cessation of cellular elongation. Pob1p is homologous to two functionally redundant Saccharomyces cerevisiae proteins, Boi1p and Boi2p, which are necessary for cell growth and relevant to bud formation. Overexpression of pob1 inhibits cell growth, causing the host cells to become round and swollen. In growing cells, Pob1p locates at cell tips during interphase and translocates near the division plane at cytokinesis. Thus, this protein exhibits intracellular dynamics similar to F-actin patches. However, Pob1p constitutes a layer, rather than patches, at growing cell tips. It generates two split discs flanking the septum at cytokinesis. The pob1-defective cells no longer elongate but swell gradually at the middle, eventually assuming a lemon-like morphology. Analysis using the pob1-ts allele revealed that Pob1p is also essential for cell separation. We speculate that Pob1p is located on growing plasma membrane, possibly through the function of actin patches, and may recruit proteins required for the synthesis of cell wall.

Pob1 Participates in the Cdc42 Regulation of Fission Yeast Actin Cytoskeleton

“…Pob1 Physically Interacts with Cdc42 in a GTP-dependent Manner To address the relationship between Cdc42 and Pob1, we first analyzed the localization of both proteins. It had been described previously that both Cdc42 and Pob1 localized to the growing poles and to the division area (Toya et al, 1999;Merla and Johnson, 2000). We found that GFP-A 8 -Cdc42 partially colocalized with Pob1 ( Figure 4A); moreover, CRIB-GFP also colocalized with Cherry-Pob1 ( Figure 4B), suggesting that Pob1 and active Cdc42 interact.…”

“…Cdc42 interacted with the C-terminal PH-containing region of Pob1 and this interaction was abolished when the PH domain was absent ( Figure 4F). These results indicate that Cdc42 interacts with the PH domain of Pob1 that has been described as essential for its function (Toya et al, 1999). Interestingly, in the two-hybrid assay pob1 ϩ not only interacted with cdc42G12V and cdc42 ϩ but also interacted with the dominant-negative cdc42T17N allele (data not shown).…”

“…This fragment contained several ORFs including pob1 ϩ , coding for an essential protein involved in cell morphogenesis. Pob1 is homologous to Boi1 and Boi2 from S. cerevisiae (Toya et al, 1999) and has 871 amino acids, including a Scr homology (SH)3 domain (residues 9 -60), a sterile alpha motif (SAM) domain (residues 248 -312), and a pleckstrin homology (PH) domain (residues 703-806). pob1-664, a thermosensitive mutant strain, becomes misshapen at 36°C (Toya et al, 1999), displaying lemon-shaped cells similar to cdc42-879 cells.…”

“…We had previously isolated several cdc42-ts mutant strains; screening them for multicopy suppressors we found Pob1, an essential protein implicated previously in polarized cell growth and cell septation (Toya et al, 1999). Overproduction of Pob1 partially suppresses the actin defects observed in the cdc42-ts mutant cdc42-879.…”

Expression and Clinical Significance of REPS2 in Human Esophageal Squamous Cell Carcinoma

“…Overexpression of REPS2 inhibits cell growth, causing the host cells to become round and swollen (Toya et al, 1999). In this study, we investigated the protein expression of REPS2 in a series of 120 clinical paraffin-embedded specimens with intact follow-up data.…”