Figure 3.

(A) Transformation of cells harboring pBar2-I-SceI-site with pSupE-I-SceI results in significant cell survival upon induction with arabinose. (B) In contrast, the same selection strain transformed with pSupE-I-SceID44S encoding an inactive endonuclease results in very low survival rates on arabinose. (C) Repeating the assay in (A) with a pBar2-I-SceI-site variant in which one critical base of the I-SceI cleavage site has been mutated (see text) also results in non-viable cells. (D) Increasing the intracellular concentration of homing endonuclease substrate by using a variant of pBar2-I-SceI-site containing four copies of the I-SceI cleavage site results in a higher level of survival compared with the two-copy variant of pBar2-I-SceI-site shown in (A).