Figure 1.

CSM and ASM of umuD and mucA. Noncleavable umuD mutations and noncleavable mucA mutations were generated by using the Stratagene Quick Change mutagenesis kit by following the manufacturer’s suggested conditions (Stratagene). The CSM from E. coli, and S. typhimurium umuD and mucA were generated in, or cloned into, pGB2 derivatives (12) (low-copy-number plasmid; three to five copies per cell) and are expressed from the wild-type umu or muc promoters. Therefore, all three CSM plasmids should express mutant proteins at or near to chromosomally encoded levels. Plasmid pJM155 also expresses UmuC, while pRW372 expresses MucB. The ASMs were generated in, or cloned into, compatible medium- or high-copy-number plasmids and are also expressed from their wild-type promoters. In contrast to the MucA ASM plasmid, which also coexpresses MucB, the E. coli and S. typhimurium ASM plasmids only express the mutant UmuD protein.