Table 2.

The spinach RRF gene, frrhcp, cannot functionally replace the E. coli RRF gene, frr

E. coli strains	Incoming plasmid	Resident plasmid	Percentage of E. coli with frrhcp retaining resident plasmid A
a	pKK233-2RRFM	A	100
b	pKK233-2RRFM	A + B	9.4
a	pRR2	A	12.5
b	pRR2	A + B	0
a	pUC19	A	100
b	pUC19	A + B	0

Plasmid pKK233–2RRFM carries Ap^r and t-frrhcp, the spinach RRF gene. Plasmid pRR2 carries E. coli frr in pUC19 (13). Two strains were transformed by these plasmids and pUC19; a, LJ2708, frr⁻, lac, [E. coli harboring plasmid A (pPEN1054sacBneo carrying Km^r and frr)]. b, LJ2211, the same as strain a harboring plasmids A and B (pMR2 carrying frr and Cm^r). Plasmid A, pKK233-2RRFM and pRR2 have the ColE1 replicon, making them incompatible with each other; plasmid B has a different replicon (pSC101 origin), making it compatible with pKK233–2RRFM. Transformants were selected by ampicillin with six single-colony isolations and tested for Km^r to examine the presence of the resident plasmid A.