Diversity among beta-tubulins: a carboxy-terminal domain of yeast beta-tubulin is not essential in vivo.

Sequences of genes for beta-tubulins from many different organisms demonstrate that they encode highly conserved proteins but that these proteins diverge considerably at their carboxyl termini. The patterns of interspecies conservation of this diversity suggest that it may have functional significance. We have taken advantage of the properties of Saccharomyces cerevisiae to test this hypothesis in vivo. The sole beta-tubulin gene of this species is one of the most divergent of all beta-tubulins and encodes 12 amino acids which extend past the end of most other beta-tubulin molecules. We have constructed strains in which the only beta-tubulin gene is an allele lacking these 12 codons. We show here that this carboxy-terminal extension is not essential. The absence of these 12 amino acids had no effect on a number of microtubule-dependent functions, such as mitotic and meiotic division and mating. It did confer dominant supersensitivity to a microtubule-depolymerizing drug.