Deletion mapping of theniiAniaD gene region ofAspergillus nidulans

SUMMARY The genetic fine-structure of the nii A nia D gene region of Aspergillus nidulans has been studied using deletion mapping. Deletions were identified as nii A nia D double mutants and comprised 1% of spontaneous chlorate-resistant mutants. All such double mutants were shown to involve deletions and their frequency was not increased by mutagenic treatment with either N -methyl- N′ -nitro- N -nitrosoguanidine or with ultraviolet light. Deletion maps of the nia D and nii A genes have been constructed. A further class of mutation was also mapped using the deletions. These crn mutations, which affect a gene whose function is as yet unknown, map on the centromere proximal side of nii A. This analysis of a eukaryote gene cluster will provide a framework upon which to base studies of the regulation of the nitrate assimilation pathway.