Schematic diagram of the exon/intron structures of the regions encoding the catalytic domain of pART family members. A) Exon/intron structures were determined by BLASTn searches of the human genome sequence with individual pART cDNA sequences. Only the exons corresponding to the catalytic domain of PARP-1 are shown. The coding region is marked in red, the 3' untranslated region (utr) is marked in white, and a blue bar marks the region corresponding to the catalytic domain. Exons are represented as boxes with the width of each box reflecting the size of the respective exon (the 3' utr is not drawn to scale). Exon numbers are given with exon 1 corresponding to the exon encoding the presumptive initiation methionine. In all cases except pART4 (VPARP) the catalytic domain is encoded by the 3' terminal exons. Exon sizes (or size of coding region in case of the 3' exons) in basepairs are indicated on top of the boxes. Introns are depicted as triangles and are not drawn to scale. Intron sizes in base pairs are indicated on top of the triangles. The position of each intron with respect to the reading frame is indicated in the triangles (0 = between codons, +1 = between codon positions 1 and 2, +2 = between codon positions 2 and 3). Conserved exon boundaries are marked by colored arrows. Codons corresponding to the H-Y-E motif in the NAD binding crevice of DT and PARP-1 (see Fig. 1) are marked by yellow circles. B) The catalytic domain as delineated in this paper is indicated by the dashed rectangle. For each pART the cDNA coding region within the catalytic domain is marked by a straight line, regions extending beyond this domain in the 5' direction (and in the 3' driection in case of pART4) are marked by dashed lines. The positions of the codons corresponding to the H, Y, E residues in the NAD-binding crevice are indicated by vertical lines. Intron phases are indicated by circles (phase 0), boxes (phase 1), and triangles (phase 2). Numbers indicate the distance in codons between the conserved histidine in β 1 and the next upstream phase 0 intron. Color-coding of conserved introns corresponds to that shown in A). Nonconserved introns are indicated in blue (filled) icons.