The Neurospora crassa gene responsible for the cut and ovc phenotypes encodes a protein of the haloacid dehalogenase family.

Light stimulation of carotenogenesis in Neurospora crassa, mediated by the White Collar proteins, is enhanced in some regulatory mutants, such as vivid and ovc. The gene responsible for the vivid mutation has been identified, but not the one responsible for the ovc phenotype. The ovc mutant is sensitive to high osmotic conditions and allelic with another mutant, cut, also osmosensitive but not affected in carotenogenesis. A phenotypic characterization of both strains is presented. Light induction of mRNA levels of the carotenoid genes al-1 and al-2, the regulatory gene wc-1 or the conidiation-specific gene con-10 is not significantly changed in the ovc mutant when compared with the wild type. We have identified the gene affected in the ovc mutant by complementation of osmosensitivity with a cosmid library. This gene, which we call cut-1, codes for an enzyme of the haloacid dehalogenase family, which includes different classes of phosphatases. cut-1 is able to restore the wild-type phenotype of the ovc and cut strains, confirming that they are affected in the same gene. DNA sequence analysis identified a point mutation in the cut mutant, leading to a truncated protein. The ovc mutant represents a deletion encompassing the entire gene and surrounding sequences. The cut-1 promoter contains putative regulatory elements involved in osmotic or thermal stress. We show that cut-1 transcription is low in illuminated or dark-grown cultures, and is induced by high osmotic conditions or by heat shock.