The SM19 gene, required for duplication of basal bodies in Paramecium, encodes a novel tubulin, η-tubulin

AbstractThe discovery of δ-tubulin, the fourth member of the tubulin superfamily, in Chlamydomonas[1] has led to the identification in the genomes of vertebrates and protozoa of putative δ homologues and of additional tubulins, ε and ζ[2–4]. These discoveries raise questions concerning the functions of these novel tubulins, their interactions with microtubule arrays and microtubule-organising centres, and their evolutionary status. The sm19-1 mutation of Paramecium specifically inhibits basal body duplication [5] and causes delocalisation of γ-tubulin, which is also required for basal body duplication [6]. We have cloned the SM19 gene by functional complementation and found that it encodes another new member of the tubulin superfamily. SM19p, provisionally called eta-tubulin (η-tubulin), shows low sequence identity with the tubulins previously identified in Paramecium, namely, α[7], β[8], γ[6], δ (this work) and ε (P. Dupuis-Williams, personal communication). Phylogenetic analysis indicated that SM19p is not consistently grouped with any phylogenetic entity