FIG 1.

(A) Representations of topA⁺ ORF delineating the encoded protein's domains D1 to D9 (adapted from references 87 and 88) and of the constructed topA alleles (three pairs) wherein the interrupted line segments represent deletions and each inverted triangle represents the pair comprising either Kan^r insertion (::Kan allele) or its FRT derivative (::FRT allele). Domains D1, D2, and D4 of Topo I are each composed of two or more polypeptide segments that are split in the linear representation but are in proximity to one another in the three-dimensional protein structure. (B) Blue-white screening assay, on LB medium, of MG1655 and MDS42 strain derivatives with the topA⁺ shelter plasmid pHYD2390 and the different topA alleles as indicated at the top of each column; the rpoB allele status is indicated to the left of each row. Examples of white colonies are marked by yellow arrows. From left to right, strains used for the panels were pHYD2390 derivatives, as follows: row 1, GJ13519, GJ15603, GJ15604, GJ15688, and GJ16921; row 2, GJ16703, GJ16813, GJ16814, GJ16815, and GJ16854; row 3, GJ12134, GJ16816, GJ16817, GJ16818, and GJ18977; and row 4, GJ16819, GJ16820, GJ16821, GJ16822, and GJ17777.