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Recombinantλgt11 vector

cDNA insert

β-Galactosidase

lacpromoter

In vitro packaging

Plate on bacterial lawn

Induce production of fusion protein-cDNA

Master plate

Pick plaque for

further analysis

Overlay nylon filter

Incubate filter with primary antibody

Wash filter

Incubate filter with labelled secondary antibody

Detection of specific antibody

Identification of cDNA in specific plaque

Fig. 6.30Screening of cDNA libraries in expression vectorlgt11. The cDNA inserted upstream from the gene for

b-galactosidase will give rise to a fusion protein under induction (e.g. with IPTG). The plaques are then blotted

onto a nylon membrane filter and probed with an antibody specific for the protein coded for by the cDNA.

A secondary labelled antibody directed to the specific antibody can then be used to identify the location (plaque)

of the cDNA.

230 Recombinant DNA and genetic analysis