Along with microarray technology, sequencing techniques such as serial analyses of gene expression (SAGE, Velculescu, Zhang, Vogelstein, & Kinzler, 1995) and its subsequent modifications (RL-SAGE, SuperSAGE, and LongSAGE) have also been used for gene expression profiling. The principle of the method is based on the detection of sequences of short cDNA fragments (10-26 base pairs depending on the version of the method) from established positions of each RNA molecule. The technique includes consecutive fragmentation of the DNA template, ligation of these fragments to form a long chain, cloning the concatemer into a bacterial vector, and sequencing this chain. The output of SAGE is a list of short sequence tags and the number of times it is observed. After being annotated into the reference genome (the digital DNA sequence database assembled by scientists as a representative example of a set of genes of Homo sapience—the human genome), these tags provide qualitative and quantitative characteristics of transcripts in the given transcriptome. So, the serial analysis of gene expression is a method for the comprehensive analysis of gene expression patterns. In contrast to
