TABLE 2.

Rates of APRT⁻ and TK⁻ APRT⁻ colony formation

Cell line(s)	Insert	Insert length (bp)	Rate of colony formatione (10−7)
			APRT−	TK−APRT−
GS3502	(CTG)17	270	7.1 ± 2.5	0.90 ± 0.10
GS3504	(CTG)98	513	6.9 ± 1.2	2.0 ± 1.4
GS3506	(CTG)183	768	9.0 ± 2.7	3.9 ± 1.7
GSC4, GSC6a	None	0	15.5 ± 2.5	0.75 ± 0.15
GS21-15b	FRT	67	14.0 ± 1.9	1.40 ± 0.27
GSE1, GSE3a	HOFRTf	114	12.3 ± 2.8	1.33 ± 0.53
GSB2, GSB5a	(GT)29	200	16.3 ± 1.8	1.55 ± 0.24
AK209c	HPRTg intron	810	14.1 ± 3.8	1.20 ± 0.40
AK784d	HPRT intron plus I-SceI	835	17.0	1.10
Mean	Non-CTG containing		14.4 ± 1.1	1.29 ± 0.14

^aResults for GSB2, GSB5, GSC4, GSC6, GSE1, and GSE3 were previously published (63).

^bResults for GS21-15 were previously published (65).

^cResults for AK209 were previously published (33).

^dResults for AK784 were previously published (66).

^eRates were determined by fluctuation analysis. For GS3502 the rates for formation of TK⁻ APRT⁻ and APRT⁻ colonies were determined from two fluctuation analyses. For GS3504 the rates were determined from four fluctuation analyses. For GS3506 the rates were determined from three fluctuation analyses. The overall mean rates of APRT⁻ and TK⁻ APRT⁻ colony formation for cell lines that did not contain a CTG insert are the averages of 17 and 16 fluctuation analyses, respectively. The standard error of the mean is shown for all rates.

^fHOFRT, the recognition sequence for HO endonuclease is located adjacent to the FRT site.

^gHPRT, hypoxanthine phosphoribosyltransferase.