TABLE 4.

Apparent binding constants (K_app) for the three KorB operators studied in vitro in the absence or presence of IncC at 150 nM

Operator (name/location)	Sequence of operator plus flanking sequencesa	Kappb (nM) for:
		KorB	KorB plus IncC
OB1 (korAp)	ACACCTTTAGCCGCTAAAACTCGTCC	7.5	2.5
OB2 (kfrAp)	GGTTTTTTAGCGGCTGAAGGGCAGGC	100	20
OB10 (trfAp/trbAp)	AGAACTTTAGCGGCTAAAATTTTGCG	2.5	<1

^aBases shown in boldface correspond to the previously defined KorB operator (3, 41). 

^bK_app was calculated as the protein concentration at which 50% of the radioactivity in the unretarded band has moved to a more slowly moving species as quantified by phosphorimager analysis. The protein concentration was calculated on the basis of KorB as a dimer but IncC as a monomer, since we have no information at present on the oligomeric state of IncC.