Molecular cloning of a novel fimbrin-like cDNA from Arabidopsis thaliana.

Fimbrin is a 68-70 kDa actin-bundling protein in animal cells and lower eukaryotes that participates in diverse morphogenetic processes by cross-linking actin filaments into bundles. Here we report the cloning by degenerate polymerase chain reaction (PCR) of ATFIM1, a 2.3 kb cDNA from Arabidopsis thaliana that codes for a novel 76 kDa fimbrin-like polypeptide (AtFim1). The predicted sequence of AtFim1 shares ca. 40% identity with nonplant fimbrins and contains two tandem repeats, each possessing a 27 amino acid region identified as a putative actin-binding domain in fimbrins and in a larger family of actin cross-linking proteins. Preceding the tandem repeats at the amino terminus of AtFim1 is a single-EF-hand-like domain with moderate homology to calmodulin-like calcium-binding proteins. AtFim1 differs from non-plant fimbrins, however, in that it contains an extended carboxy-terminal tail of ca. 65 amino acids. ATFIM1 is encoded by a single gene, although sequencing of two partial fimbrin-like expressed sequence tag (EST) clones indicates that Arabidopsis contains at least two fimbrin-like proteins. Northern blot analysis and reverse-transcription PCR (RT-PCR) demonstrated that ATFIM1 is expressed in all major organs examined (roots, leaves, stems, flowers and siliques). This is the first report of the cloning of a full length plant gene that encodes a putative actin filament-bundling protein.