FIGURE 1.

Gene and domain structure of the DS epimerases. A, schematic view of the DSE and DSEL genomic structure. Exons are shown with rectangles, and introns with curved lines. Coding regions are shown as filled boxes. B, domain structure of the two epimerases, showing a common N-terminal epimerase domain followed by two distinct domains of different length (of unknown function) and, in the case of DS-epi2, by an O-sulfotransferase-like domain. The locations of signal peptides (SP) and predicted transmembrane regions (TM) are also shown. A potential 3′-PAPS-binding site is depicted with a straight line. C, amino acid conservation of the 3′-PAPS-binding site is shown by alignment (generated with ClustalW) to the protein sequences of human C6ST-1, HS-3OST1, and C4ST-1. Catalytic amino acids are marked with asterisks.