Prof Peter Chantler
Molecular Biology of the Cell
d. Library screening
The final step involves library screening, facilitating selection of the particular clone from the library that you are interested in.
Plating out the phage on to bacterial lawns is the first step of the screening process. Replicas are produced by placing absorbent paper, nitrocellulose or nylon membranes, over the agar plates in such a way that the pattern of plaques on the original plate is maintained. Each replica is then incubated with an appropriate nucleic acid probe that is labelled in some way (eg. radiolabelling) so as to facilitate selection. If the probe is a radiolabelled fragment of DNA, the location of the positive plaques may be detected through exposure to X-ray film, this process being known as autoradiography.
Typically, these will be grown up and plated out at least twice more so as to ensure that one is dealing with monoclonal material.
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Course updated 6 Apr 2004