cDNA library

cDNA is produced from fully transcribed mRNA found in the nucleus and therefore contains only the expressed genes of an organism.

In eukaryotes, a poly-(A) tail (consisting of a long sequence of adenine nucleotides) distinguishes mRNA from tRNA and rRNA and can therefore be used as a primer site for reverse transcription.

Once mRNA is purified, an oligo-dT primer (a short sequence of deoxy-thymidine nucleotides) is bound to the poly-A tail of the RNA.

Once selected, stocks of the bacteria are created which can later be grown and sequenced to compile the cDNA library.

Genomic DNA libraries provide more detailed information about the organism, but are more resource-intensive to generate and keep.

Linkers are short, double stranded pieces of DNA (oligodeoxyribonucleotide) about 8 to 12 nucleotide pairs long that include a restriction endonuclease cleavage site e.g. BamHI.

Following "sticky end" ligation of the insert into the vector the resulting recombinant DNA molecule is transferred into E. coli host cell for cloning.