Genetic Manipulation 221Figure 9.3 Recombinant Baculovirus
reporter genes to indicate whether or not the signals are ‘switched on’ allowing
the ‘foreign’ DNA to be expressed. There are many reasons which are difficult
to predict, why even a perfectly constructed gene may not be functional, such as
the consequence of the exact site of insertion in the genome; hence the need for
inbuilt controls.
Reporter genes
There are many such genes in common use and these usually code for an enzyme.
The most common isβ-galactosidase, mentioned above. This enzyme, supplied
with the appropriate reagents, may also catalyse a colour change by its activity on
a variety of chemical compounds typified by orthonitrophenolgalactoside (ONPG)
which changes from colourless to yellow on hydrolysis in much the same way as
the blue/white screening described above for the cloning vector, pGEM.Other
reporter genes produce enzymes which can cause the emission of light such as
theluciferaseisolated from fireflies, or whose activity is easy and quick to assay
like the bacterialβ-glucuronidase (GUS), which is probably the most frequently
used reporter gene in transgenic plants. Reporter genes can only be a guide to
the process of transcription and translation occurring in the cell and it has been
acknowledged for some time that care must be exercised to avoid misinterpreting
data (Pessi, Blumer and Haas. 2002).