ABSTRACT
The problem of searching through a library to find a desired cloned DNA fragment is affected significantly by the relative complexity, or number of different fragments present in the library. Because expression of eukaryotic genes in prokaryotic hosts is uncommon, screening by positive selection is rarely used for characterization of bacterial transformants containing eukaryotic genes. In screening methods that use antibodies, antibodies against the desired protein are allowed to react with extracts from colonies of interest, and then the antibody-protein complexes are visualized with other reagents. Because the entire protein need not be present for recognition by an antibody, specialized expression vectors have been developed that simplify the use of antibodies in screening. The production of fusion proteins ensures that proteins encoded by cloned DNA inserts will be produced in bacteria and made available to antibodies during testing. Colony blotting procedures that use antibodies as probes allow hundreds of transformants to be examined in search of a desired gene fragment.
