What term describes a molecule that activates the transcription of a gene by inactivating a genetic repressor?

The appropriate term for a molecule that activates transcription by inactivating a genetic repressor is indeed "inducer." Inducers play a crucial role in regulating gene expression in prokaryotes and eukaryotes. They bind to repressors or other regulatory proteins, causing a conformational change that diminishes or eliminates the repressor's ability to bind to the operator or other regulatory sequences of DNA. As a result, this alleviates the repression of transcription, thus allowing RNA polymerase to access the gene and initiate transcription.

This regulatory mechanism is essential in various biological processes, such as those involving operons in bacteria (like the lac operon). Here, the presence of an inducer like lactose can bind to the repressor protein, effectively disabling it. Therefore, transcription of the genes necessary for lactose metabolism can proceed. Understanding the function of inducers is key to grasping how gene expression can be fine-tuned in response to environmental and cellular signals.