All cells regulate gene expression in response to changes in the external environment. For
unicellular organisms, specific mechanisms have evolved to allow these cells to metabolize
various fuels based on their availability in the external milieu. In part, these mechanisms
involve conditional transcription of genes encoding enzymes unique to specific metabolic
pathways in the presence of appropriate nutrients. The study of such control mechanisms
has led to several of the classic paradigms for transcriptional regulation present in today's …