What Is Biotechnology? - Biotechnology and Your Health: Pharmaceutical Applications - page 12

Viruses are natural vectors that take over cells and make them into
virus-producing factories, a process that often kills the cell. Some
viruses have been used as vectors for biotechnology after their genetic
information has been changed to remove the instructions that permit
the production of full-fledged new viruses. There are bacterial viruses
called bacteriophage that can be used as genetic engineering vectors—
that is, after they have been modified to make them useful but not
harmful to the bacteria.
To insert the gene cassette into the vector, the vector DNA is cut
with a matching RE that creates sticky ends so that it will accept the
gene and promoter. Another protein called DNA ligase is used to
rejoin, or stitch up, the pieces of DNA, joining the cut ends.
All that is left to be done is to add the engineered vector to a
group of the bacteria, yeast, or other cells that have been treated to
make their outside membrane porous enough to allow the plasmid
or other vector DNA to enter. At this point, the cell has been engi-
neered to make the desired product (Figure 1.4).
How can scientists tell that the cell has been successfully engi-
neered? It is possible for mistakes to occur. Some of the RE-clipped
pieces may not have lined up at the correct spot, or may have lined up
with each other, but the scientists are prepared for this. In addition to
the product gene and its on-switch, the scientists include a gene for
a protein that would make the engineered cell stand out. This may
be a gene for a protein that breaks down an antibiotic, or a gene for
a protein that makes the cells give off fluorescent light. Whatever type
of gene is used, the protein produced by the extra gene lets scientists
distinguish cells that were successfully changed from those that were
not. Now scientists have cultures of engineered cells that can be grown
to large numbers and make the desired protein.
Living Factories
Every cell—whether bacterium, yeast, plant, insect, or human—is a
protein factory, among other things. Cells produce the proteins for