Make way for the Age of SAGE. Introduced in 1995 by Kenneth Kinzler and Bert Vogelstein of the Johns Hopkins University in Baltimore, Md., SAGE, or Serial Analysis of Gene Expression, is a quantitative method of gene expression analysis based on the idea that an mRNA transcript can be identified by just a short (9-14 base pair) subfragment.1

In the technique, mRNA is isolated, copied into cDNA, tagged at the 3' end with biotin, and then cut with a restriction enzyme. The tagged fragments are then isolated with streptavidin-coated beads, amplified, ligated into a single molecule, and sequenced. The enumeration of each "tag" indicates the level of expression of the gene it represents. The technique has several advantages over microarray analysis, as it can detect genes with no prior sequence information, is sensitive for low-abundance genes, and provides digital quantification of gene expression. The public database SAGEmap...

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