Isolation and characterization of phototropism mutants of Phycomyces insensitive to ultraviolet light.

Phototropism mutants of the zygomycete fungus Phycomyces blakesleeanus were isolated on the basis of their loss of responsivity to UV light. Four of these mutants had retained a partial sensitivity to near-UV and to blue light. Gravitropism and the avoidance response were unaffected in these mutants. One mutant, A909, had lost most of its sensitivity to near-UV and blue light while the sensitivity to far-UV light was only slightly affected. Additionally, the gravitropic and the avoidance responses were significantly reduced in A909. A complementation analysis of the five strains of Phycomyces with known phototropism mutants indicated that strains A896, A897, and A898 were defective in the madA gene, and that A905 was affected in the madC gene. In strain A909 the input, as well as the output, of the transduction chain is affected.