No evidence for intra-allelic complementation at the osmotic-1 locus of Neurospora crassa

The osmotic-1 (os-1) locus of Neurospora crassa encodes a protein with homology to bacterial and plant two-component histidine kinases. The os-1 protein appears to be an osmo-sensor and is the first step in a MAP kinase cascade that regulates intra-cellular osmolarity and cell-wall synthesis (Alex L, Borkovich K, Simon MI. Hyphal development in Neurospora crassa: involvement of a two-component histidine kinase Proc Natl Acad Sci U S A. 93:3416-21. 1996; Schumacher M, Enderlin C, Selitrennikoff CP. The osmotic-1 locus of Neurospora crassa encodes a putative histidine kinase similar to osmosensors of bacteria and yeast. Curr Microbiol. 34:340-7. 1997). Mutants defective at the os-1 locus are sensitive to a number of hyper-osmotic conditions, including 4% NaCl (Mehadevan P. and Tatum E. Relationship of the major constituents of the Neurospora crassa cell wall to wild-type and colonial morphology. J. Bacteriol. 90:1073-1081. 1965). In other organisms, e.g., prokaryotes, similar histidine kinases exist as homodimers (C. Tomomori C, Tanaka T, Dutta R, et al. Solution structure of the homodimeric core domain of Escherichia coli histidine kinase EnvZ Nat. Struct. Biol. 6:729. 1999) in which an extracellular signal induces the autophosphorylation of a histidyl residue of one member of the dimer. The phosphoryl group is subsequently transferred to an aspartyl residue of the other dimer pair, triggering a regulatory kinase cascade.