Molecular dissection of alleles of the osmotic-1 locus of Neurospora crassa.

Two-component histidine kinases of bacteria, plants, and fungi are involved in the regulation of intracellular events in response to changes in external environmental conditions. Fungal histidine kinases play important roles in osmoregulation, in vivo and in planta virulence, and sensitivity to certain classes of antifungals. The osmotic-1 (OS-1) locus of Neurospora crassa encodes a predicted protein with homology to histidine kinases and appears to be an osmosensor. Mutants of the OS-1 locus are hypersensitive to salt and are strongly resistant to dicarboximide antifungals. Molecular analysis of each of eight OS-1 mutants revealed that seven resulted from amino acid changes in a domain of the protein known as the linker region. These results indicate that the linker region of fungal two-component histidine kinases is essential for proper functioning of the kinase.