What Are the Functions of an Expression Vector?

Expression vectors are a key component of genetic engineering. They are plasmids or small sections of DNA inserted into living cells. The inserted plasmid expresses, hence the name, a single gene which produces a single protein. This new protein could turn on or turn off some chemical process, cause something new to be produced by the cell, or make the cell relate differently to its neighbors.

What Expression Vectors Do

• All cells have the same DNA. The reason cells behave differently is that different patterns of genes are blocked in different cells. Expression vectors insert a new unblocked gene into the DNA of selected cells. Like all genes, this new gene directs the building of a protein. Most proteins are either enzymes or receptors.

  Enzymes control chemical reactions, so the new gene might stop some undesirable process associated with a disease or it may allow some new process to happen. These processes may involve what the cell produces. For example, one of the first successful expression vectors caused cells to produce more insulin.

  Receptors are proteins that attach themselves to cell walls and act as gatekeepers between the cell and the rest of the body. They can affect how a cell relates to other cells or to the blood stream. In short, a successfully implanted expression vector makes a cell behave differently.

Ancillary Functions

• Most gene expressions are more complicated than "one gene, one protein." The expression vector must supply certain ancillary DNA information as the switches that turn the gene expression process on and off. Also, many proteins are made in parts--which means several genes--and assembled elsewhere in the cell.

  The expression vector is really a complex of genetic materials that requires a good working knowledge of the biological pathways involved. It is also important that the expression vector be implanted in the right kind of cell--one that has the right suite of genes unblocked. For example, when used for cloning--a common use for expression vectors--the vector must be inserted in a stem cell.

Functional Examples

• Expression vectors play a key part in cloning--building a copy of an animal from a single cell. Expression vectors also allow modification of foods so that tomatoes and peaches ripen later after being picked--so they can be stored and shipped. Scientists have altered fish genes so fish grow faster and are healthier to eat. They have modified plant crops to produce their own insecticides and herbicides. The genes of some bacteria have been modified to make them eat pollutants, and the genes of other bacteria have been modified to make them produce medicines.

  Some of the most interesting expression vector modifications involve inserting genes from fireflies into plant crops which has produced tomatoes and other plants that glow in the dark.