CLONING OF THE PACB-TE-R REGION FROM PLASMID MIP233 (INCHI3) AND THEIR EXPRESSION IN ESCHERICHIA-COLI TON, TOL MUTANTS

A region of the plasmid Mip233 (incompatibility group HI3) encoding th e phenotypes of resistance to the channel-forming colicins (character PacB) and potassium tellurite (Te-r), was cloned and studied. Both pro perties are contained in an insert of 2.2 Kbp, being the smallest func tional clone (pB22) isolated so far. E. coli DH5 alpha pB22 transforma nts exhibit resistance to the colicins as well as to high levels of te llurite (> 1000 mu gml(-1)). Results suggest that they are genetically linked forming an inducible operon. pB22 does not show significant ho mology with DNA from other H plasmids. Tests using E. coli ton and tol mutants harbouring recombinant pB22 indicate that the product of gene tolC, but not that of tonB, is required for the expression of the Pac B and Te-r phenotypes.