In this issue

The `multi-tubulin hypothesis' formulated a quarter of a century agopostulated that eukaryotes use different forms of the protein tubulin toconstruct a wide variety of microtubule-based structures. Since then, workersin the field have identified a host of distinct αβ-tubulin isotypesand post-translational modifications that can influence microtubule structureand function. Keith Gull and co-workers review our understanding of the rolesof these different tubulins and re-examine the multi-tubulin hypothesis in thelight of recent work. Studies of the C. elegans β-tubulinisotype MEC-7, for example, indicate that it endows the axons of touchreceptor neurones with a distinct, 15-protofilament organization. Additionalevidence for the specialization of different forms of tubulin arises from therecent demonstration that microtubules in the basal bodies ofDrosophila sperm contain only β1-tubulin whereas the spermflagellar axoneme contains only β2-tubulin. Similarly, γ-tubulinappears to have a specific role in nucleation of microtubules. The tubulinsuperfamily is now known to extend to at least seven members. Gull andco-workers...