Genetic Engineering - Cloning, DNA, Stem Cells Pros and Cons
Molecular genetics

The future technology

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.

  1. A mutant strain must be available for the gene in question

  2. 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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