FIG. 3.

Sequence alignment of confirmed nucleoside N-ribohydrolases and homologous predicted proteins. Residues with a proposed role in catalysis are shown as white letters on a black background. An asterisk above such positions indicates involvement in chelating Ca²⁺ at the active site of Cf-IUNH; + below the sequence indicates involvement in hydrogen bonding to the 2′-, 3′-, and 5′-hydroxyl groups of ribose in Cf-IUNH (see Discussion). Amino acids which are highly conserved (greater than 90%; PAM250 residue weight table) are shaded in dark gray; conservation of greater than 75% is indicated by lighter gray shading. The predicted protein sequences show the following sequence identities when compared with Urh1p: C. fasciculata inosine-uridine nucleoside hydrolase (accession number U43371), 23%; T. brucei subsp. brucei purine-specific nucleoside hydrolase (AF017231), 13%; L. major nonspecific nucleoside hydrolase (39), 26%; E. coli Yeik (U000007), Ybek (AE000169), and Yaaf (D10483), 24, 25, and 24%, respectively. Two hypothetical genes from S. pombe (S. pombe 1, Z69795; S. pombe 2, U33010) show 23 and 21% identity, respectively.