cDNA Libraries

Messenger RNA (mRNA) 1s a complex mixture of easily degraded molecules representing the processed (splrced, polyadenylated, and capped) transcripts from genes that are active in a given tissue or cell type In the construction of a cDNA library, RNAdependent DNA polymerase (reverse transcnptase, RT) 1s used to convert mRNA into double-stranded cDNA molecules suitable for insertion into vectors (plasmlds or bacteriophage) that can be propagated in prokaryotes Because cloning the vectors and hence cDNA libraries can be propagated mdefimtely, usually in the bacterial host Escherzchza colz , this results in an effectively permanent and mexhaustlble library or bank of cDNA clones representing the original mRNA population The real u&y of this, however, 1s the ability to select or screen for specific cDNAs and thus isolate a cDNA copy of a particular mRNA in a pure state