Photocontrol of the polypeptide composition ofEuglena

Abstract

Two-dimensional gel electrophoresis resolved total cellular protein fromEuglena gracilis Klebs var.bacillaris Cori into 650 polypeptides detectable by silver staining. Exposure of dark-grown restingEuglena to light for 72 h increased the relative amounts of 79 polypeptides and decreased the relative amounts of 72 polypeptides. Four polypeptides whose level increased upon light exposure were undetectable in the bleached mutant W₃BUL. Since W₃BUL has lost most if not all of its chloroplast genome, these polypeptides may be coded by the chloroplast genome. Although the majority of the polypeptides studied appear to be coded by the nuclear or mitochondrial genomes, seven polypeptides which were present in W₃BUL were not detectable in another chloroplast-DNA-deficient, bleached mutant, W₁₀BSmL. It appears that a number of nonchloroplast genes are no longer expressed in this mutant. Exposure of dark-grown resting cells of the bleached mutant, W₃BUL, to light increased the relative amounts of 12 polypeptides and decreased the relative amounts of 14 polypeptides. Since W₃BUL lacks detectable protochlorophyll(ide), the chloroplast photoreceptor, the levels of these polypeptides are regulated by light acting through a nonchloroplast photoreceptor. Exposure of cells to light had no detectable effect on the relative amounts of those polypeptides which were present in W₁₀BSmL, even though W₁₀BSmL has a nonchloroplast photoreceptor. EitherEuglena contains multiple nonchloroplast photoreceptors, some of which are absent from W₁₀BSmL, or the nonchloroplast photoreceptor present in W₁₀BSmL is uncoupled from some of the events normally controlled by that photoreceptor.