FIG. 5.

Protection of MmeI enzyme by substrate (pUC18) from chemical modification by 2,3-butanedione. Endonucleolytic activity of MmeI was measured using pUC18 DNA as a substrate. Three experiments were performed. Plot a (crosses) shows the activity of MmeI measured without modification with 2,3-butanedione (positive control); plot b (squares) shows the results of the substrate protection experiment, in which MmeI was preincubated with the substrate DNA (pUC18) before it was modified with 2,3-butanedione. Plot c (triangles) shows the activity of the enzyme in the presence of the 2,3-butanedione (without prior substrate protection).