Regulation of the lac operon in E. coli (see Chapter 16) and regulation of the GAL system in yeast are analogous in that they both serve to adapt cells to growth on different carbon sources. However, the transcriptional changes are accomplished very differently. Consider the conceptual similarities and differences as you address the following.

Compare and contrast the cis-regulatory elements of the lac operon and GAL gene system.

Key Concepts

Cis-Regulatory Elements

Cis-regulatory elements are regions of non-coding DNA that regulate the transcription of nearby genes. They include promoters, enhancers, and silencers, which interact with transcription factors to control gene expression. In the context of the lac operon and GAL system, these elements play crucial roles in determining how genes respond to environmental signals, such as the presence of specific sugars.

Lac Operon

The lac operon is a well-studied example of gene regulation in E. coli, consisting of genes required for the metabolism of lactose. It is regulated by the presence of lactose and glucose, involving a promoter and an operator where the repressor protein binds. When lactose is present, it binds to the repressor, allowing transcription to occur, showcasing a classic example of negative regulation.

GAL Gene System

The GAL gene system in yeast regulates the metabolism of galactose and involves a different set of cis-regulatory elements compared to the lac operon. It includes a promoter and upstream activating sequences that interact with specific transcription factors, such as Gal4. The system exemplifies positive regulation, where the presence of galactose activates transcription, highlighting the diversity in regulatory mechanisms across different organisms.