OXYGEN AND THE CONTROL OF GENE-EXPRESSION

The respiration of oxygen, while essential to aerobic organisms for th e generation of energy, leads to the formation of reactive oxygen inte rmediates (ROIs) as harmful byproducts. ROIs damage nucleic acids, lip ids and proteins. Therefore, protective mechanisms against elevated in tracellular ROI levels, referred to as oxidative stress, have evolved. These include the activation of transcription factors which elevate t he expression of protective enzymes. Eukaryotic cells have also evolve d the ability to specifically generate ROIs following stimulation with various agents. In these cases, ROIs are used as second messengers to activate gene expression. Here we will discuss both prokaryotic and e ukaryotic transcription factors that respond to ROIs. In addition, tra nscription factors will be described that are activated by either expo sure to antioxidants, which reduce the intracellular ROI concentration , or by hypoxia, the absence of oxygen.