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Question
Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign DNA in addition to a selectable marker?
Solution
Transformation is the process of introducing a fragment of DNA into a host bacterial cell. Normally, genes encoding antibiotic resistance, such as ampicillin and tetracycline, are considered useful selection markers for discriminating between transformed and non-transformed bacterial cells. In addition to these selectable markers, another selectable marker has been designed to distinguish between transformed and non-transformed bacterial cells based on their ability to produce colour in the presence of a chromogenic material. A recombinant DNA is inserted into the coding sequence of β-galactosidase, a reporter enzyme. If the plasmid in the bacterium does not have an insert, the presence of a chromogenic substance gives blue-coloured colonies. The presence of an insert results in insertional inactivation of β-galactosidase and, therefore, the colonies do not produce any colour. These colonies are marked as transformed.
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