The Kavar(D) dominant female-sterile mutations of Drosophila reveal a role for the maternally provided alpha-tubulin4 isoform in cleavage spindle maintenance and elongation.

The dominant-negative female-sterile Kavar(D) mutations and their revertant kavar(r) alleles identify the alphaTubulin67C gene of Drosophila melanogaster, which codes for the maternally provided alpha-tubulin(4) isoform. The mutations result in the formation of monopolar, collapsed spindles (each with two nearby centrosomes, a tassel of microtubules and overcondensed chromosomes), thus revealing a novel function for alpha-tubulin(4) in spindle maintenance and elongation. Molecular features of the two Kavar(D) alleles and a kavar(null) allele are described and models for their actions are discussed.