The lactose system inKlebsiella aerogenesV9A: 4. A comparison of thelacoperons ofKlebsiellaandEscherichia coli

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Abstract
SUMMARY: Klebsiella aerogenesV9A contains twolacoperons, one chromosomal and one borne by the Lac plasmid,FKlac. It is shown that the plasmid Lac repressor resembles that ofEsherichia coliin that it represses theE. colioperon but is inactivated by melibiose. In contrast, the chromosomal Lac repressor of V9A is unable to repress theE. colioperon or the FKlacoperon, but is converted into an active repressor of both these operons on becoming bound to melibiose. The chromosomal Lac repressor is able to repress its own operon whether or not it is bound to melibiose, but is inactivated by isopropyl-β-D-thiogalactoside. These results support the hypothesis that theKlebsiellaLac plasmid was derived from an ancestralE. colichromosome.