PrfA is a protein that serves as a global regulator of virulence genes in Listeria, a bacterium that can cause severe food poisoning. Below host body temperatures PrfA mRNA exists in a conformation that hides the ribosome binding site. Upon entry into a host and a rise in temperature, hydrogen bonds in the mRNA break, exposing the ribosome binding site. What level of gene regulation is controlling the expression of this transcription factor? Is this transcription factor an activator or a repressor