The Scope and Limitation of Marker Rescue
Although marker rescue can be used to obtain clues
of many genes, the technique is subject to two limitations.
- A mutant strain must be available for the gene in
question
- A medium on which only the wild-type can survive
is needed
Marker rescue is applicable for most genes that code
for biosynthetic enzymes, as clones of these genes can
be selected on minimal medium in the manner described
for trpA.
However, the technique is not limited to E.coli
nor even bacteria; auxotrophic strains of yeast and
filamentous fungi are also available, and marker rescue
has been used to select genes cloned into these organisms.
In addition, E. coli auxotrophs can be used as hosts
for the selection of some genes from other organisms.
Often there is sufficient similarity between equivalent
enzymes from different bacteria, or even from yeast,
for the foreign enzymmes to function in E. coli, so
that the cloned gene is able to transform the host to
wild-type.
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