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

Abstract

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 [γ- 32P]ATP at 0°C for 1 s with blue light (450 nm, 6 μmol/m 2/s or 420 nm, 80 μmol/m 2/s). The reaction was stopped at 5 s of incubation at 0°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 stimulate 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.