FIGURE 1.

(A) Sequence windows surrounding donor and acceptor splice sites, l_e nucleotides within exon, and l_i nucleotides within intron. (B) Arrangements of complementary boxes. Each of the two complementary boxes (5′-box and 3′-box) can be located either at donor or at acceptor splice site. If both 5′- and 3′-box (filled circles) are located at the same splice site (different splice sites), the corresponding structure is referred to as cis-structure (trans-structure, respectively). There is no limit on the distance between boxes. Complementary boxes are denoted by dotted arcs. The two-letter code denotes the location of boxes so that, for instance, DA stands for Donor-Acceptor location of 5′- and 3′-boxes (in this order).