Figure 4
Roles of replication, repair, and recombination functions in expansion. Multiple independent cultures of the indicated genotype were plated on lactose minimal medium. Strains are all MG1655 derivatives. All except the ones labeled "sc" (for single copy) bear the the (lacIZ33Y)2-cat duplication. Strains labeled "red+" bear the phage λ red recombination genes, which replace the recC-ptr-recB-recD gene cluster in the E. coli chromosome. Except for the red substitution, the lexA alleles, and the recAo281 operator mutation, all the alleles are nulls made by substituting an antibiotic resistance element for the coding sequence of the gene.