Final answer:
The lac operon's activity in prokaryotes like E. coli is regulated through inducible control involving promoter and operator regions, being activated when glucose is low and lactose is available.
Step-by-step explanation:
The regulation of the lac operon is a crucial aspect of prokaryotic gene expression and occurs at the transcriptional level. It is controlled by proteins that bind to the operon's promoter and operator regions. There are two key conditions that determine the activity of the lac operon in bacteria such as E. coli. Firstly, the level of glucose must be very low or non-existent, and secondly, lactose must be present. In the absence of glucose, the catabolite activator protein (CAP) binds to the promoter, enhancing the binding of RNA polymerase and leading to the transcription of genes necessary for lactose metabolism. In the presence of lactose, it inactivates the lac repressor protein, preventing it from binding to the operator and thus allowing transcription to proceed. This inducible system ensures efficient use of energy and resources, activating the lac operon only when glucose is scarce, and lactose is available as an alternative energy source.