Fig. 1.

Diagrams of Easter processing. (A) Processing of the wild-type Easter zymogen at the zymogen cleavage site in embryos results in rapid formation of a covalent complex between the catalytic serine of Easter and serpin27A that is not sensitive to reducing agents, in contrast to the disulfide bond linking the pro-domain (gray) and the catalytic domain (with catalytic triad residues indicated). (B) Processing of an Easter zymogen in which the catalytic serine is mutated to alanine results in production of a stable but inactive catalytic domain fragment, which cannot form a covalent complex with serpin27A. Sizes of fragments recognized by the Easter antibody are indicated at right.