Figure 2.

The lethality of ΔtopA cells can be suppressed by increased levels of DNA topoisomerase III, but not by overexpression of recG. (A) Arabinose-induced expression of topB, which codes for DNA topoisomerase III, leads to formation of white colonies. The smaller colony size indicates that the suppression is only partial. Increased levels of DNA topoisomerase III are toxic for E. coli cells, leading to reduced numbers of blue colonies as well as aberrant colony morphologies (compare the two enlarged colonies in Ai and Aii). (B) Increased levels of RecG support growth of ΔtopA cells only marginally