USA Biology Olympiad (USABO) Practice Exam

The promoter region of a prokaryotic gene is located ______ to the gene and is the binding site for ______.

1. 3'...DNA polymerase

2. 5'...RNA polymerase

3. 5'...DNA ligase

4. 3'...RNA ligase

The correct answer is: 5'...RNA polymerase

The promoter region of a prokaryotic gene is essential for the initiation of transcription, where the transcription machinery assembles to begin synthesizing RNA from a DNA template. It is located upstream, or 5' to the gene, which means it precedes the coding sequence and is crucial for directing the RNA polymerase to the correct site for transcription to start. In prokaryotes, RNA polymerase, the enzyme responsible for synthesizing RNA, binds to the promoter region to recognize the specific sequence, ensuring that transcription occurs in the correct direction and at the right gene. This binding is a key step in the regulation of gene expression, allowing the cell to control which genes are expressed under various conditions. Understanding the role of the promoter and its position also highlights the importance of transcription factors and other regulatory proteins that may interact with this region to enhance or inhibit transcription. This relationship is fundamental in both prokaryotic and eukaryotic organisms, but the mechanisms can differ significantly. In this context, the choice that states the promoter is 5' to the gene and is the binding site for RNA polymerase accurately depicts the mechanics of prokaryotic gene expression.