expression vector
Cloning a gene into an ordinary vector copies the DNA, but it does not necessarily make the cell read that gene and build its protein. An expression vector is a vector designed to do exactly that: not just carry and copy a gene, but actively drive the host cell to transcribe and translate it into protein.
What sets it apart are the control elements built in around the insertion site. An expression vector supplies a strong promoter to switch transcription on, along with the signals a host needs to translate the resulting messenger RNA efficiently. Often the promoter is inducible, meaning the researcher can keep the gene quiet and then flip it on with a chemical cue, so the cell grows first and makes the protein on command.
Expression vectors are the workhorse of producing proteins to order. They let bacteria, yeast, or cultured animal cells churn out a chosen protein in bulk — for research, for industrial enzymes, or for medicines like insulin and antibody drugs. Getting good expression often requires matching the vector and its signals to the particular host, since what works smoothly in bacteria may need adjustment in an animal cell.
To produce human growth hormone, the gene is placed in an expression vector with a strong bacterial promoter, and induced bacteria then synthesize the hormone in large quantities.
A built-in promoter turns a cloned gene into a protein factory.
A plain cloning vector aims only to maintain and replicate DNA, while an expression vector additionally carries the promoter and other signals needed to produce protein; the right choice depends on whether you want the DNA, the protein, or both.