Schematic diagram of the exon/intron structures of pART family members of distantly related organisms. A) Exon/intron structures were determined by BLASTn searches of the genome browsers using the pART cDNA sequences. The positions of codons corresponding to the H Y E motif in the NAD-binding crevice of diphtheria toxin are marked by yellow circles. The position of the conserved glycine and arginine pair of residues within the WGR domain is marked in blue. Coding regions for catalytic and other domains are indicated by colored bars. Conserved introns are marked by colored arrows. B) The diagram contains only those introns that are conserved in at least two distantly related species. Color-coding of the introns corresponds to that shown in A). The position of codons encoding/corresponding to the H, Y, E residues in the NAD binding crevice are indicated by vertical lines. The position of each intron with respect to the codon is indicated by circles (phase 0 introns), boxes (phase 1 introns), and triangles (phase 2 introns). Coding regions for catalytic and other selected domains are indicated by colored lines as in A).