What methods can verify protein expression from a cloned gene?

• A. SDS-PAGE and Western blotting
• B. Sanger sequencing
• C. Northern blot analysis
• D. Quantitative PCR

Answer: (A)

Verifying protein expression means confirming that the cloned gene actually produces the protein product. Separating proteins by size with SDS-PAGE shows whether a protein of the expected molecular weight is present, but it doesn’t identify it. Western blotting adds that identification step by probing the layed-out proteins with an antibody specific to the target protein, so a signal confirms both expression and the protein’s identity, often with some size confirmation.

The other methods don’t directly prove protein production. Sanger sequencing checks the DNA sequence of the cloned gene to ensure the insert is correct, but it doesn’t reveal whether that gene is translated. Northern blot analyzes RNA to measure transcript levels, not the protein itself. Quantitative PCR quantifies RNA levels (or DNA copies, depending on setup), giving transcriptional data rather than evidence of the protein product.