FIG. 7.
Segregational stabilization of an unstable plasmid in E. coli C2110 polA by parABS of P. aeruginosa. (A) Rate of loss of vector pOG04 and its derivatives with parS2/3 only (pABB71) and with a tacp-parAB transcriptional fusion and parS2/3 (pABB72), determined as described in Material and Methods. The values presented were calculated relative to the plasmids present in the initial overnight cultures. These values were about 30% for pOG04 and all of its derivatives, with the exception of pABB72, for which 50% plasmid retention occured. No effect of IPTG was observed for all plasmids, with the exception of pABB72. To simplify the diagram, data for cultures without IPTG are shown only for pABB72. Data for pABB70, carrying the tacp-parAB transcriptional fusion but lacking a parS site, were the same as for pOG04 and pABB71 (data not shown). (B) E. coli C2110 polA (pABB72 parS tacp-parAB lacIq) from a logarithmic culture grown without selection for 3 h. The cells were stained with DAPI and treated with primary anti-ParB antibodies and secondary FITC-conjugated anti-rabbit IgG antibodies. Only cells with ParB foci are presented.