The objective of this research project is to identify and isolate molecules that serve as blue-light photoreceptors in the fungus Phycomyces. Special attention will be given to phototropism mutants (genes madA to madH) including those (madB and madC) with defective photorecptor(s). Recent spectrophotometric and biochemical analyses have revealed modifications in the photorecptor mutants, notably light-induced absorbance changes (LIAC) with specific alterations in madC mutants. LIAC will be measured in vivo and in vitro and will serve as a spectroscopic assay for the photoreceptor(s). Biochemical characterization and purification of the photoreceptor(s) will employ two-dimensionl gel electrophoresis and fast protein liquid chromatorgraphy (FPLC) in conjunction with spectroscopic and genetic assays. Flavoproteins will receive special consideration as probable candidates for blue light photoreceptors. Electrophoresis and chromatography will also be applied to proteins found to be altered in other behavioral mutants (madA, madB, and madE). Additional mutants will be sought and incorporated in the project. Although blue-light responses are widespread among plants, funji, and other organisms, the photoreceptor molecules remain to be identified. Phycomyces offers special advantages, in view of its unmatched sensitivity and the availability of behavioral mutants. Identification of photoreceptors in Phycomyces will greatly promote the understanding of photosensory transduction in connection with its various light responses (phototropism, light- growth response, photocarotenogenesis, and photodifferentiation). The results on Phycomyces should lead the way to identification of blue light photoreceptors in other organisms.
