Purification of DEG15wt (left) and DEG15S580A (right) by affinity chromatography with Ni2+-nitrilotriacetic acid. Asterisk indicates 76-kD full-length protein, arrow indicates 47-kD product of putative self-cleavage, and circle marks 40-kD truncated DEG15. Purification of DEGH392A and DEG15D491A was similar to DEG15S580A; all other purifications were similar to DEG15WT. The major fragment band at 40 kD was absent in DEG15S237A. M, Marker; F, flow through; W, wash fraction; E, elution fraction.