Gibberellin (GA) is a plant hormone that promotes seed germination by activating transcription of the α-amylase gene. In the absence of GA, a DELLA protein binds to a transcription factor, preventing it from stimulating transcription. When GA is present, it triggers the breakdown of the DELLA protein, freeing the transcription factor to increase transcription of the α-amylase gene. In bacteria, the lac operon controls the production of enzymes needed to metabolise lactose.
Describe the differences between structural genes and regulatory genes, and between repressible and inducible enzymes. Using the lac operon as an example, describe how gene expression is controlled in prokaryotes. Also describe how a transcription factor (such as the one in the GA pathway) increases the rate of transcription of a target gene in eukaryotes.