FIG. 4.
Implication of serine 38 and lysine 76 in the active site of S. pneumoniae signal peptidase I. (A) Autoradiography of 35 S-labeled prestreptokinase and its cleavage by wild-type and mutant signal peptidase I. (B). SDS-PAGE and Coomassie brilliant blue staining of purified prestreptokinase and its cleavage by wild-type and mutant signal peptidase I. The assays were performed as described in the text. Lane 1, prestreptokinase only; lane 2, prestreptokinase + wild-type signal peptidase; lane 3, prestreptokinase + mutant S38A; lane 4, prestreptokinase + mutant K76A. Pre-Ska and mSka, prestreptokinase and mature streptokinase, respectively.