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.

[6] cDNA library lacks the non-coding and regulatory elements found in genomic DNA.

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.