Final answer:
An activator without an activating domain may need a coactivator to help in gene transcription, and is not considered a repressor unless it actively inhibits transcription.
Step-by-step explanation:
An activator that does not have an activating domain may require a coactivator with an active domain to initiate transcription. Activators are proteins that enhance the interaction between RNA polymerase and a specific promoter, aiding in the process of gene transcription. A mutation in an activator that results in the loss of the activation domain, while retaining the DNA-binding domain, can lead to the protein blocking the transcription site, thus preventing the wild-type transcription factor from activating gene expression. This mutant version does not necessarily become a repressor; instead, it might act by hindering the activity of other necessary transcription factors.
In prokaryotic cells, repressors, activators, and inducers are regulatory molecules that can affect operon expression by binding to DNA sequences adjacent to the genes they control. While repressors bind to operator regions to inhibit transcription, activators bind to promoter sites to enhance transcription. Enhancers, found in eukaryotic cells, are distant binding sites for activator proteins, which facilitate the initiation of transcription by altering the DNA's shape and allowing activators to interact with the transcription initiation complex.