Journal Article

<i>Tetrahymena</i> Fimbrin Localized in the Division Furrow Bundles Actin Filaments in a Calcium-Independent Manner

Shin Shirayama and Osamu Numata

in The Journal of Biochemistry

Published on behalf of The Japanese Biochemical Society

Volume 134, issue 4, pages 591-598
Published in print October 2003 | ISSN: 0021-924X
Published online October 2003 | e-ISSN: 1756-2651 | DOI:
Tetrahymena Fimbrin Localized in the Division Furrow Bundles Actin Filaments in a Calcium-Independent Manner

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In cytokinesis, the contractile ring constricts the cleavage furrow. However, the formation and properties of the contractile ring are poorly understood. Fimbrin has two actin-binding domains and two EF-hand Ca2+-binding motifs. Ca2+ binding to the EF-hand motifs inhibits actin-binding activity. In Tetrahymena, fimbrin is localized in the cleavage furrow during cytokinesis. In a previous study, Tetrahymena fimbrin was purified with an F-actin affinity column. However, the purified Tetrahymena fimbrin was broken in to a 60 kDa fragment of a 70 kDa full length fimbrin. In this study, we investigated the properties of recombinant Tetrahymena fimbrin. In an F-actin cosedimentation assay, Tetrahymena fimbrin bound to F-actin and bundled it in a Ca2+-independent manner, with a Kd of 0.3 µM and a stoichiometry at saturation of 1:1.4 (Tetrahymena fimbrin: actin). In the presence of 1 molecule of Tetrahymena fimbrin to 7 molecules of actin, F-actin was bundled. Immunofluorecence microscopy showed that a dotted line of Tetrahymena fimbrin along the cleavage furrow formed a ring structure. The properties and localization of Tetrahymena fimbrin suggest that it bundles actin filaments in the cleavage furrow and plays an important role in contractile ring formation during cytokinesis.

Keywords: Key words: actin, Ca2+, cytokinesis, fimbrin, Tetrahymena.; Abbreviations: AtFim1, Arabidopsis fimbrin; CaM, calumodulin; EF-1α, elongation factor-1α; Fim1p, Schizosaccharomyces pombe fimbrin.

Journal Article.  5215 words.  Illustrated.

Subjects: Biochemistry

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