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, a team at the Human Genome Center, Institute of Medical Science,
University of Tokyo developed an oligo-capping
method to obtain full-length cDNAs, the information of which has been
partly deposited in public databases. In this
study, they 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 corresponded to
cDNA sequences of known genes (8,996 genes) and are presented in the
DataBase of Transcriptional Start Sites (DBTSS).
Sequence comparison between the DBTSS entries and those of the reference
sequence database, RefSeq, revealed that
4,802 (34.2 %) of RefSeq sequences should be extended towards the 5' ends.
The team also mapped each sequence on
the human draft genome sequence to identify its transcriptional start site,
which provided more detailed information
on distribution patterns of transcriptional start sites and adjacent
regulatory regions.