Final answer:
An activator is the transcription factor that enhances gene expression by helping RNA polymerase to bind to the promoter. Operons that are transcribed and translated continuously to maintain constant protein levels are constitutively expressed.
Step-by-step explanation:
A transcription factor that enhances gene expression is called a activator. In the context of gene expression regulation, a repressor is a transcription factor that suppresses transcription, while an activator is a transcription factor that increases transcription of a gene by facilitating RNA polymerase binding to the promoter. Operons can be constitutively expressed, meaning they are transcribed continuously, providing the cell with constant levels of protein products without needing induction or repression by external stimuli.