How to get the best of dbEST

Expressed sequence tags (ESTs) are nucleotide sequences generated from the ends of randomly selected cDNA clones. The remarkable expansion of EST efforts in the past seven years[ 1 , 2 , 3 ]has undoubtedly led to a revolutionary change in the strategies used by molecular geneticists for identifying and cloning novel genes. More than 1 200 000 entries generated from different tissues and species are now stored in the public EST database (dbEST)[ 4 , 5 ], maintained at the National Center for Biotechnology Information (NCBI). Human and mouse sequences form the majority of the data held in this collection, with 833 000 and 237 000 entries, respectively (as of 25 October, 1997)[ 6 ]. For most of the clones, ESTs have been generated at both ends and the corresponding sequence traces can be easily retrieved for quality checking[ 7 ]; furthermore, it is possible to obtain in a few days most of the EST cDNA clones, such as the ones generated by the IMAGE consortium and The Institute for Genomic Research (TIGR)[ 1 , 8 ], from international distributors[ 9 ]. EST clones represent useful molecular tools for gene characterization experiments, expression studies, and expression of recombinant proteins. In most cases, a single EST clone (average insert size around 1.5 kb) does not span the entire coding region of a gene. However, before starting any experimental procedure aimed at the isolation of the remaining part of the transcript, it must be pointed out that several bioinformatic tools exist that allow one to obtain full-length transcript information and refined chromosomal mapping assignment.