Abstract
There has been little information about molecular mechanisms involved in cytokinesis in unicellular green algae. Septins comprise a GTPase family involved in cytokinesis in eukaryotes except plants. Here we report NbSep encoded on the nuclear genome of N. bacillaris. NbSep contains a septin-specific GTPase domain, of which sequence identity is 41% with CDC10 (Saccharomyces), 45% with Peanut (Drosophila), and 42% with Sept2 (human). A phylogenetic analysis demonstrates that NbSep belongs to group 1 which contains all subfamilies of fungal septins and one of animal septin subfamilies. The septins assemble of GTP into filaments with the hydrolysis in vivo and in vitro. The incubation of a recombinant NbSep with GTP yielded ~2 μm filamentary structures in length. N. bacillaris cells grow from 3-6 μm in length, dividing by binary fission. An intense fluorescent signal from immunostained NbSep was observed as a ring at the middle of the dividing cell.
