SF-assemblin in Chlamydomonas: Sequence conservation and localization during the cell cycle

Previously, SF-assemblin has been identified as the filament-forming component of the striated microtubule-associated fibers (SMAFs), which emerge from the basal bodies in several green flagellates. We have sequenced cDNAs coding for SF-assemblin from Chlamydomonas reinhardtii and C. eugametos. Comparison of the deduced amino acid sequences with the previously described green algal SF-assemblins shows identities between 54 and 71%, indicating a strong drift in sequence. Cells of C. reinhardtii were analyzed by double immunofluorescence using polyclonal anti-SF-assemblin and anti-α-tubulin. In interphase cells, SF-assemblin is associated with all four microtubular flagellar roots. During mitosis the SF-assemblin-based cytoskeleton is reorganized; it divides in prophase and is reduced to two dot-like structures at each spindle pole in metaphase. During anaphase, the two dots present at each pole are connected again. In telophase we observed an asymmetrical outgrowth of new fibers. These observations suggest a role for SF-assemblin in reestablishing the microtubular root system characteristic of interphase cells after mitosis.