Question

A protein coding gene of an organism with unknown genome sequence can be isolated from

• A. Genomic library
• B. cDNA library
• C. Amplification with gene specific primer
• D. Amplification with degenerate primers

Hint:

Genomic libraries are used to study promoters, regulatory elements, and introns, whereas cDNA libraries are preferred for cloning functional protein-coding sequences for expression.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Isolating a functional protein-coding gene from an unsequenced organism requires a strategy that captures transcribed sequences without genomic intron interference.

Step 2: Detailed Explanation:
- A cDNA (complementary DNA) library is constructed by reverse transcribing mature mRNA into DNA.
- Since mRNA undergoes post-transcriptional splicing, the cDNA molecules represent only the expressed, intron-free protein-coding regions (exons).
- When the genome sequence of an organism is completely unknown, genomic libraries are difficult to screen due to the presence of large non-coding introns.
- Screening a cDNA library allows direct isolation of the full-length coding sequence (open reading frame) of the target gene.

Step 3: Final Answer:
A protein-coding gene from an unsequenced organism is best isolated from a cDNA library.