The transcriptional gene control in eukaryotes is mediated by

The correct option is "trans-acting factors binding to cis-acting elements".

Step-by-Step Explanation:

1. Understanding Eukaryotic Transcription Regulation:
In eukaryotic organisms, transcription is a highly regulated process that determines when and how much of a specific gene product (RNA) is produced. This regulation is primarily mediated by the interaction between two key components: regulatory DNA sequences and protein molecules that bind to them.

2. What are Cis-acting Elements?
Cis-acting elements are specific, non-coding DNA sequences located on the same chromosome as the gene they regulate (hence "cis", meaning "on the same side"). Examples of cis-acting elements include promoters, enhancers, and silencers. These elements serve as physical binding sites on the DNA molecule.

3. What are Trans-acting Factors?
Trans-acting factors are molecules—most commonly proteins known as transcription factors—that are encoded by genes located elsewhere in the genome. Because they are synthesized in the cytoplasm and diffuse to their target sites, they can regulate genes located anywhere in the cell (hence "trans", meaning "across"). These factors recognize and bind specifically to the cis-acting elements.

4. Mechanism of Mediation:
For transcription to be initiated, activated, or repressed, trans-acting transcription factors must physically bind to the corresponding cis-acting regulatory DNA sequences. Once bound, these factors interact with RNA polymerase and other co-activators or chromatin remodeling complexes to facilitate or inhibit transcription. Therefore, the transcriptional gene control is mediated by the binding of trans-acting factors to cis-acting elements.