(A) Multiple sequence alignment of ORF-16 and diverse members of the vertebrate ADP-ribosyltransferase family (Pfam PF01129). Sequences are indicated by their SwissProt names. The established secondary structure for ART2.2 (PDB entry 1GXZ ) is indicated by colored bars. PHD secondary structure prediction for ORF-16 is indicated below. (The results of a consensus secondary structure prediction applying various other methods can be found as part of the supplementary material on our website.) The sequence alignment was basically adopted from the RPS-BLAST alignment of the CD-Search hit. The first 30 amino-terminal and the last 10 carboxy-terminal residues not covered by the CD-Search hit were manually aligned. It must be noted, that the alignment is, thus, based on sequence similarity alone and was not edited considering any structural information. Critical residues of the typical R-S-E motif (see text) are marked by an arrow. Disulfide forming cysteines are marked by a filled circle. (B) Structure of ART2.2 from rat. The structure consists of a mainly alpha helical amino-terminal part and a carboxy-terminal part dominated by beta-sheets. The NAD binding site is formed by β-2, β-5, β-6 and β-8. Numbering and colors of the secondary structural elements are the same as in (A).