Although the information of cDNAs is indispensable for analyzing gene function, most of the cDNA sequences stored in
current databases are imperfect in the sense that they lack the precise information of 5' end termini.
To overcome this difficulty, we have developed the oligo-capping method to obtain full-length cDNAs,
the information of which has been partly deposited in public databases.
In this study, we further constructed human cDNA libraries enriched in clones containing the cap structure to systematically
explore the 5' end structure of expressed genes.
Of about 284,687 5' end sequences obtained, 155,304 have been corresponded to cDNA sequences of known genes (8,996 genes)
and are presented in our new database, DataBase of Transcriptional Start Sites (DBTSS; http://dbtss.hgc.jp/home.html).
Sequence comparison between our entries and those of a reference sequence database, RefSeq, revealed that
4,802 (34.2 %) of RefSeq sequences should be extended towards the 5' ends.
We also mapped each sequence on the human draft genome sequence to identify its transcriptional start site,
which provides us with more detailed information on distribution patterns of transcriptional start sites and adjacent regulatory regions.