118. TATA box involved in the initiation of transcription is located in the:
A. Promoter region
B. Enhancer region
C. Exon region
D. Intron region

Detailed Explanation:

The TATA box is a conserved DNA sequence found in the core promoter region of many genes. It plays a crucial role in the initiation of transcription by RNA polymerase II in eukaryotic cells.

Key Points:

• The TATA box is usually located about 25–35 base pairs upstream of the transcription start site.

• It serves as a binding site for the TATA-binding protein (TBP), a subunit of the transcription factor IID (TFIID) complex.

• Once TBP binds, it helps recruit other transcription factors and RNA polymerase II, facilitating the formation of the pre-initiation complex.

Location Analysis:

• Promoter region: Correct. The TATA box is a part of the core promoter and helps initiate transcription.

• Enhancer region: Incorrect. Enhancers regulate gene expression from a distance and do not contain the TATA box.

• Exon/Intron regions: Incorrect. These are parts of the gene that are transcribed into RNA, while the TATA box is upstream of the transcription start site.

Correct Answer:

A. Promoter region

The TATA box is an essential sequence element that signals the starting point for transcription, making the promoter region its correct location.