IGD: a resource for intronless genes in the human genome.

Intronless genes (IGs) fraction varies between 2.7 and 97.7% in eukaryotic genomes. Although many databases on exons and introns exist, there was no curated database for such genes which allowed their study in a concerted manner. Such a database would be useful to identify the functional features and the distribution of these genes across the genome. Here, a new database of IGs in eukaryotes based on GenBank data was described. This database, called IGD (Intronless Gene Database), is a collection of gene sequences that were annotated and curated. The current version of IGD contains 687 human intronless genes with their protein and CDS sequences. Some features of the entries are given in this paper. Data was extracted from GenBank release 183 using a Perl script. Data extraction was followed by a manual curation step. Intronless genes were then analyzed based on their RefSeq annotation and Gene Ontology functional class. IGD represents a useful resource for retrieval and in silico study of intronless genes. IGD is available at http://www.bioinfo-cbs.org/igd with comprehensive help and FAQ pages that illustrate the main uses of this resource.