A mixture of total eukaryotic cellular RNA molecules (rRNA, mRNA, and tRNA) is hybridized to oligo dT chemically attached to a support matrix (green column). PolyA-containing messenger RNA, mRNA (blue), is retained on the column while the ribosomal RNA, rRNA (red), and transfer RNA, tRNA (green), flow through. Hydrogen bonding is then disrupted, allowing the collection of mRNA free of rRNA and tRNA