e-Tubulin was discovered in the human genome database as a "beta tubulin-like" cDNA [9]. Like 5-tubulin, it has since been identified in other vertebrates, and single-celled organisms with cilia or flagella, but not in invertebrates, fungi or higher plants. In animal cells e-tubulin localizes to the sub-distal appendages of the mature centriole [28]. The sub-distal appendages are only assembled on the newer of the two original centrioles at the G2/M transition, so e-tubulin is asymmetric with respect to the centrioles prior to G2/M. This staining pattern is similar to that reported for ninein [29], and an increasing list of proteins (for example, see [30]). Experiments in which e-tubulin was depleted from a frog egg extract centro-some duplication assay showed that it is required for centriole formation, but not for microtubule nucleation or mitotic aster formation [28].

Dutcher et al. [31] showed that the product of the BLD2 gene is the Chlamydo-monas ortholog of e-tubulin, that e-tubulin localized to basal bodies, and that the mutant was defective for forming the doublet and triplet microtubules of the basal bodies. Similar experiments with gene silencing of e-tubulin in Paramecium by Dupuis-Williams et al. [32] also showed defects in basal body microtubule formation.

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