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FYVE-related domain found in protein spire homolog 1 (Spire1) and similar proteins Spire1 is encoded by gene spir-1, which is primarily found to be expressed in the developing nervous system and in neuronal cells of the adult brain, as well as in the fetal liver and in the adult spleen. It functions as a new essential factor in asymmetric division of oocytes. It mediates asymmetric spindle positioning by assembling a cytoplasmic actin network. It is also required for polar body extrusion by promoting assembly of the cleavage furrow. Moreover, it cooperates synergistically with Fmn2 to assemble F-actin in oocytes. Spire1 contains an N-terminal protein-interaction KIND domain, WH2 actin-binding domains, a Rab GTPase-interaction Spir-box, and a C-terminal FYVE membrane-binding domain. The FYVE domain resembles a FYVE-related domain that is structurally similar to the canonical FYVE domains but lack the three signature sequences: an N-terminal WxxD motif (x for any residue), the central basic R(R/K)HHCRxCG patch, and a C-terminal RVC motif, which form a binding pocket that specifically binds the phospholipid phosphatidylinositol 3-phosphate (PtdIns3P or PI3P).
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