Question

Choose the correct sequence of different regions on a typical eukaryotic DNA segment when we go from the upstream to the downstream of a transcription start point.
A. Initiation site
B. CAAT box
C. Enhancer
D. TATA box
Choose the correct answer from the options given below:

• A. B, D, A, C
• B. A, C, B, D
• C. B, A, D, C
• D. C, B, D, A

Hint:

Think of approaching a gene like landing a plane. The \textbf{Enhancer} is the distant airport beacon. The \textbf{CAAT box} is the outer marker. The \textbf{TATA box} is the runway threshold. The \textbf{Initiation site} is the touchdown point. The sequence is always from far to near: Enhancer \(\rightarrow\) Proximal Elements (CAAT) \(\rightarrow\) Core Promoter (TATA) \(\rightarrow\) Start Site.

Answer 1

The Correct Option is D

Step 1: Concept Overview:
Eukaryotic genes possess intricate regulatory regions. The task is to order these elements based on their position relative to the transcription start site, from upstream (5' direction, further away) to downstream (towards and past the start site).
Step 2: Element Location:
Identifying each element's position relative to the transcription start site (+1):


C. Enhancer: A distal control element. Enhancers can be located thousands of base pairs upstream or downstream of their target gene, generally being the most upstream element.

B. CAAT box: A proximal control element, typically located -80 to -70 base pairs upstream of the start site.

D. TATA box: A core promoter element, positioned very close to the start site, usually at -35 to -25 upstream.

A. Initiation site (INR): The transcription start point, designated +1. It's the most downstream element listed.

Step 3: Solution:
Ordering the elements from most upstream (farthest, most negative position) to most downstream (+1) yields: Enhancer \(\rightarrow\) CAAT box \(\rightarrow\) TATA box \(\rightarrow\) Initiation site. This corresponds to the sequence C, B, D, A.