Genetic analysis of a Drosophila microtubule-associated protein.

The 205-kD microtubule-associated protein (205K MAP) is one of the principal MAPs in Drosophila. 205K MAP is similar to the HeLa 210K/MAP4 family of MAPs since it shares the following biochemical properties: it is present in several isoforms, has a molecular mass of approximately 200 kD, and is thermostable. Furthermore, immuno-crossreactivity has been observed between mouse MAP4, HeLa 210K, and Drosophila 205K MAP. Currently, there is little information concerning the biological function of this group of nonmotor MAPs. We have used a classical genetic approach to try to identify the role of the 205K MAP in Drosophila by isolating mutations in the 205K MAP gene. An F2 lethal screen was used to acquire deficiencies of 100EF, the chromosomal location of the 205K MAP gene. Drosophila bearing a homozygous deficiency for the 205K MAP region are fully viable and show no obvious phenotype. A recently developed polymerase chain reaction screen was also used to recover five P-element insertions upstream from the 205K MAP gene. Western blot analysis has shown that these insertions result in hypomorphic mutations of the 205K MAP gene. As was seen with animals that have no 205K MAP, these mutations appear to have no phenotype. These data unambiguously demonstrate that the 205K MAP gene is inessential for development. These results also suggest that there may exist protein(s) with redundant function that can substitute for 205K MAP.