Light signals are transduced to the phosphorylation of 15 kDa proteins in Neurospora crassa

A microsomal fraction prepared from the mycelia of the band (bd) strain of Neurospora crassa showed enhanced phosphorylation of two small proteins with molecular masses of around 15 kDa (ps15) by the irradiation of the reaction mixture containing [gamma-32P]ATP at 0 degrees C for 1 s with blue light (450 nm, 6 mumol/m2/s or 420 nm, 80 mumol/m2/s). The reaction was stopped at 5 s of incubation at 0 degrees C after blue light irradiation. The light effect could not be detected in ps15, when a microsomal fraction from a blind mutant, wc-1 or wc-2 was used. The mixing followed by homogenization of the microsomal fractions from wc-1 and wc-2 restored the activity to simulate the phosphorylation of ps15 by blue light. The phosphorylated amino acid residue of ps15 was unstable when the proteins on a nylon membrane were exposed to an acid or alkaline solution, suggesting that the phosphorylated residue was aspartic acid. The other phosphorylated protein with a molecular mass of 70 kDa (p70) showed no light effect in the phosphorylation and the phosphorylated residue was estimated to be histidine, since it was stable in alkaline solution.