Detection of Proteins in a Genomic Library
A genomic library could have the entire gene sequence (and more) inserted into the Lac-Z gene. Usually the insertion takes place behind the promoter of the Lac-Z gene. The E. coli RNA polymerase will obviously recognize the promoter so that the gene can be turned on to give the blue color if there is no insert. The insert will not interfere with the initiation of transcription but the message encoded will have the additional sequences encoded by the insert. This abnormal message will not encode a normal protein for the following reasons.
2) If the genomic library is from a eukaryote, the gene will likely have introns. These introns will probably not be spliced from the mRNA because the bacteria lack the ability to perform this. After all, the bacteria does not have introns in their genes.
Consequently, a genomic library from a eukaryote will not be expected to make the protein encoded by the gene of interest and the antibody screening method will not work. However, if the genomic library is from a prokaryote, the method may work if no false start codons are encountered in the message from the recombinant Lac-Z gene.