Transcription unit

Options

A. starts with TATA box
B. starts with palindrome regions and ends with rho factor
C. starts with promoter region and ends in terminator region
D. starts with C A A T region.

Explanation

### Step-by-Step Solution:

1. **Understanding the Transcription Unit**:
- A transcription unit is defined as the segment of DNA that is transcribed into RNA. It encompasses the entire length of the RNA molecule produced, from the start of transcription to the end.

2. **Identifying Key Components**:
- The transcription unit consists of two main components:
- **Promoter Region**: This is the starting point for transcription where RNA polymerase binds to initiate transcription.
- **Terminator Region**: This is the endpoint of transcription where RNA polymerase stops and releases the newly synthesized RNA.

3. **Analyzing the Options**:
- **Option 1**: Starts with TATA box - The TATA box is part of the promoter region, but it does not define the entire transcription unit.
- **Option 2**: Starts with palindrome region and ends with Rho factor - This is incorrect as Rho factor is involved in termination but does not define the transcription unit.
- **Option 3**: Starts with promoter region and ends in terminator region - This correctly describes the transcription unit.
- **Option 4**: Starts with CAAT region - The CAAT box is also part of the promoter but does not define the transcription unit.

4. **Conclusion**:
- Based on the analysis of the options, the correct answer is **Option 3**, which states that the transcription unit starts with the promoter region and ends with the terminator region.