Minor introns, or U12-type introns, were initially identified based on their divergent terminal dinucleotide sequences (Jackson, 1991). Soon thereafter, it was found that these introns in fact contained an entirely different 5' splice site and branch point sequence compared to the other class of introns, called major introns (Hall and Padgett, 1994; Dietrich et al., 1997). As such, these minor introns could not be spliced by the major spliceosome. Indeed, the Steitz lab then identified several components of a different splicing machinery, which could splice these minor introns, and this was called the minor spliceosome (Tarn and Steitz, 1996).
MIDB contains the most recent information on minor introns and the genes they are found in, also called MIGs (minor intron-containing genes). The minor introns in this database were identified for several model organisms using position-weight matrices, and this will soon be expanded to other species. Besides useful information on the coordinates of these minor introns and MIGs, this database also provides additional information that may be of use, such as expression pattern data and disease associations. Individual genes and the corresponding minor introns can be queried by selecting a species and typing the (partial) name of a MIG. Importantly, one can also provide the Ensembl ID to query genes and any of the NCBI listed synonyms.