Interacting genes that affect microtubule function: the nc2 allele of the haywire locus fails to complement mutations in the testis-specific beta-tubulin gene of Drosophila.

A mutation that fails to complement certain alleles of the testis-specific beta 2-tubulin gene (B2t) of Drosophila melanogaster maps to a separate locus, haywire, located at 3-34.4 map units in polytene region 67E3-F3. Second-site non-complementing mutations such as haync2 and B2t alleles could identify genes that encode products that participate in the same functions or that interact in the same structure. Consistent with a structural interaction between the hay gene product and beta 2-tubulin, the genetic interaction between haync2 and B2t requires the presence of the mutant hay gene product; a deficiency for the hay region complements the same alleles of B2t that haync2 fails to complement. haync2 is a recessive male sterile mutation in a genetic background that is wild type at the B2t locus. Homozygous males have defects in meiosis, flagellar elongation and nuclear shaping, the three major microtubule-based processes in which the testis-specific beta 2-tubulin participates. The haync2 allele also has effects outside of spermatogenesis. It is a temperature-sensitive semilethal mutation, and homozygous haync2 females have reduced fertility. These phenotypes are consistent with a role for the haywire gene product in general microtubule function. Analysis of second-site non-complementing mutations such as haync2 offers a genetic tool for analysis of interacting proteins in complex assemblies.