Long-lost relatives reappear: identification of new members of the tubulin superfamily.

The identification and analysis of new members of the tubulin superfamily has advanced the belief that these tubulins play important roles in the duplication and assembly of centrioles and basal bodies. This idea is supported by their distribution in organisms with centrioles containing triplet microtubules and by recent functional analysis of the new tubulins. delta- and epsilon-tubulin are found in most organisms that assemble triplet microtubules. delta-tubulin is needed for maintaining triplet microtubules in Chlamydomonas and Paramecium. epsilon-tubulin is needed for centriole and basal body duplication and is an essential gene in Chlamydomonas. The distribution of eta-tubulin is more limited and has been found in only four organisms to date. Phylogenetic analysis suggests that it is most closely related to delta-tubulin, which suggests that delta- and eta-tubulin could have overlapping functions.