1. DNA library Genomic libraryenomic library cDNA library Genomic Library: DNA fragments representing the entire genome of an organism. cDNA Library :Complementary DNA molecules synthesized from mRNA molecules in a cell. All mRNA present in cell Collection of cloned DNA fragments

2. Isolation of RNA Isolated Cytoplasmic RNA consists of ribosomal RNAs (rRNAs)ribosomal RNAs transfer RNAs (tRNAs).transfer RNAs mRNAs with 3′ poly(A) tails

3. 3′ poly(A) tails of mRNA hybridize to oligo-dT covalently coupled to the column matrix

5. Preparation of cDNA from mRNA

7. EcoRI methylase, a modification enzyme that catalyzes addition of a methyl group to two adenines in the EcoRI recognition sequence. The methylated restriction site is not cleaved by EcoRI, assuring that a cell making this restriction enzyme does not destroy its own DNA.enzyme

8. Sticky End