Multiple amino acid sequence alignment of the C-terminal region of 23 yCCR4-related proteins, extended to three Mg2+-dependent endonucleases, i.e. HAP1 (human; accession number M80261), exoIII (E. coli; accession number AAC74819) and DNAseI (bovine ; accession number M60606). Only blocks containing more than three positions where residues display at least 60% similarity (calculated from a distance BLOSUM62 matrix, SQX program, Infobiogen) are shown, with the remaining of the sequence indicated by residue numbers in parenthesis. Positions with strict identity are shaded dark grey, and those with >60% similarity light grey. For the other aligned proteins (HAP1, exoIII, and DNAseI), residues identical to those strictly conserved in the yCCR4-related proteins are also shaded dark grey. Residues conserved in the yCCR4-related proteins but not found in the presently aligned endonucleases or other Mg2+-dependent endonuclease-fold containing proteins (not shown) are marked with an asterisk. The secondary structure elements (α-helix and β-strand) for HAP1 and/or exoIII (see Fig. 4 in  and Fig. 1 in ) are indicated under the alignment. Important residues involved in the Mg2+-dependent endonuclease activity are indicated as follows: empty circles for phosphate binding residues, filled circles for Mg2+ binding residues, triangles for catalytic residues, and squares for residues involved in orientation and/or stabilization of the catalytic residues. Amino acid positions above the alignment are for h.nocturnin.