简介

At a time when the genomes of many species have been sequenced completely, a fundamental

resource expected by many researchers is a simple list of all of an organism's genes. A gene list,

together with associated physical reagents and electronic information, allows one to begin to

investigate the ways in which many genes interact in the complex system of the organism. However,

many species of medical and agricultural importance have not yet been prioritized for

genomic sequencing, and expressed cDNAs have provided the primary source of gene

sequences. Furthermore, when the genomic sequence of an organism becomes available, a collection

of cDNA sequences provides the best tool for identifying genes within the DNA sequence.

Thus, we can anticipate that the sequencing of transcribed products will remain a significant area

of interest well into the future.

The eara of high-throughput cDNA sequencing was initiated in 1991 by a landmark study from

Venter and his colleagues. The basic strategy involves selecting cDNA clones at random and

performing a single, automated, sequencing read from one or both ends of their inserts. They

introduced the term EST to refer to this new class of sequence, which is characterized by being

short (typically about 400–600 bases) and relatively inaccurate (around 2% error). The use of

single-pass sequencing was an important aspect of making the approach cost effective. In most

cases, there is no initial attempt to identify or characterize the clones. Instead, they are identified

using only the small bit of sequence data obtained, comparing it to the sequences of known genes and other ESTs. It is fully expected that many clones will be redundant with others already