Table 3.

Effect of subculture conditions on pyrF elimination and generation of false positives

Subculture	Medium	Frequency of occurrence (%)a
		5-FOA resistantb	False positivec	Revertantd
Procedure A
1	LB	0.01 ± 0.00
2	LB	0.45 ± 0.42
3	LB	0.29 ± 0.28	63 ± 5
4	+5-FOAe	59 ± 53	7.8 ± 6.0	61 ± 17
Procedure B
1	MMf	4.5 ± 0.9
2	MM	5.5 ± 3.9
3	MM	5.5 ± 2.9	86 ± 9
4	+5-FOA	9.4 ± 5.6	8.1 ± 13	68 ± 12

^aThe values shown are means ± SD from four independent experiments using transconjugants that had integrated pGAM47-bgaB.

^bThe values shown are the number of colonies growing from subculture aliquots on MM plates containing 10 mg/liter uracil and 5-FOA compared with the number on LB plates (i.e., 5-FOA-resistant cells per total cells).

^cThe values shown are the number of clones growing on MM plates without uracil per 48 5-FOA-resistant clones (i.e., uracil-prototrophic cells per 5-FOA-resistant cells).

^dThe values shown are the number of clones exhibiting white colonies on LB plates with 200 mg/liter X-Gal per 32 uracil-auxotrophic clones generated (i.e., MK72 revertant cells per total cells from which pyrF had been eliminated).

^eMM containing 1 mg/liter uracil and 5-FOA.

^fMM containing 10 mg/liter uracil.