Effect of plasmid clones on recombinant mutant Y. pestis topoisomerase I expression and growth rates Western blot analysis of expression of mutant Y. pestis topoisomerase I in the presence of control vector and clone pAQ5 (a) or pInter (b). Exponential phase cultures were treated with 0.002% arabinose for 2.5 h. Total cellular protein was analyzed by SDS PAGE and Western blot with mouse monoclonal antibodies against E. coli topoisomerase I (EcTOP). This antibody recognizes the highly homologous Y. pestis topoisomerase I (YpTOP) and its partially degraded product (YpTOP*).(C) Growth of BW27784 transformed with vector, pInter, pInterD1 and pInterD2 in LB. Absorbance was measured in a 96 well microplate at 37°C every 20 min using the Perkin Elmer 7000 Plus BioAssay Reader with the filter set at 590 nm and shaking for 10 min before each measurement.