Which feature does an expression vector have that makes it suitable for protein production?

• A. Strong promoter, ribosome binding site, selectable marker, origin of replication
• B. Only a fluorescent tag
• C. Random promoter without RBS
• D. No selection marker or replication origin

Answer: (A)

To produce proteins efficiently in a host, an expression vector must support high transcription, effective translation, and reliable maintenance in cells. A strong promoter drives robust transcription of the gene, boosting mRNA levels and potential protein yield. The ribosome binding site is crucial for initiating translation, so the mRNA is efficiently converted into protein. A selectable marker lets you identify and keep only the cells that actually carry the plasmid, making it easier to isolate producers and maintain the plasmid in the population. The origin of replication ensures the plasmid is copied inside the host, so the plasmid is maintained across generations and the gene is present in enough copies to sustain production.

Other options fall short because a fluorescent tag alone doesn’t promote high expression, a random promoter without an RBS may transcribe but cannot efficiently translate into protein, and having no selection marker or replication origin means the plasmid won’t be stably maintained or easily identified in producers.