Translational regulation of the synthesis of euglena fumarase by light and ethanol

Ethanol addition or the exposure of dark-grown resting Euglena to light produced a transient increase in the rate of fumarase synthesis as measured by pulse-labeling with [(35)S]sulfate and immunoprecipitation. The half-life of fumarase in the dark and in the light was similar. In the plastidless mutant W(3)BUL, fumarase synthesis was transiently induced by light indicating that fumarase induction is regulated by a nonchloroplast photoreceptor. In the plastidless mutant W(10)BSmL, light exposure did not increase the rate of fumarase synthesis while the addition of ethanol transiently induced fumarase synthesis. The nonchloroplast photoreceptor regulating fumarase synthesis appears to be absent or nonfunctional in W(10)BSmL. In vitro translation of Euglena RNA in a rabbit reticulocyte lysate showed that fumarase is synthesized as a precursor of 61.5 kilodaltons which is 1.5 kilodaltons larger than the mature protein. The levels of translatable RNA for fumarase were similar in the dark and after light exposure or ethanol addition. The transient increase in the in vivo rate of fumarase synthesis after light exposure or organic carbon addition was not accompanied by a concomitant increase in the level of translatable RNA for fumarase. The synthesis of fumarase in dark grown resting Euglena upon light exposure and ethanol addition is controlled at the translational rather than at the transcriptional level.