Final answer:
Transcriptional gene control in eukaryotes is mediated by trans-acting factors, such as transcription factors, binding to cis-acting elements, which are DNA sequences associated with the gene being regulated.
Step-by-step explanation:
The transcriptional gene control in eukaryotes is primarily facilitated by trans-acting factors binding to cis-acting elements. These trans-acting factors, which include various transcription factors, bind specifically to DNA sequence motifs near the promoter of the gene, known as cis-acting elements, on the same chromosome as the gene. These elements can be proximal or distal to the gene they regulate. The specific binding of transcription factors to promoter regions and enhancer sequences initiates or enhances the transcription of the target gene.
In eukaryotes, general transcription factors and specific regulatory transcription factors play a critical role in the process. General transcription factors are required for RNA polymerase to bind to the promoter. The binding of additional regulatory transcription factors to cis-acting elements further refines transcriptional control. These interactions can either increase or prevent transcription, depending on the presence and combination of enhancers or repressors. Therefore, the correct answer to this question is that transcriptional gene control in eukaryotes is mediated by trans-acting factors binding to cis-acting elements.