How can recombinant DNA technology achieve expression of a human protein in bacteria?

• A. By using a bacterial expression vector with a suitable promoter, ribosome binding site, and codon optimization, plus perhaps a signal sequence and fusion tags.
• B. By inserting the human protein directly into bacterial genome without vectors.
• C. By expressing in bacteria using eukaryotic promoters only.
• D. By expressing human protein only in mitochondria.

Answer: (A)

Expressing a human protein in bacteria relies on a bacterial expression system that controls transcription and translation of the gene. A plasmid-based expression vector provides a bacterial promoter to drive transcription, a ribosome binding site to initiate translation, and codon optimization to match the bacterial tRNA pool, which improves yield and accuracy of the protein. Including a signal sequence can route the protein to the periplasm or secretion pathway if needed, and fusion tags assist with solubility, purification, and detection. Altogether, these elements create a functional unit in the bacterial host that enables production of the human protein.

Inserting the human gene directly into the bacterial genome without a vector isn’t practical for achieving high-level, controllable expression. Bacteria won’t recognize human promoters, so relying on them won’t drive expression in a bacterial system. Bacteria don’t have mitochondria, so expressing a human protein in that context isn’t applicable here.