Table 4. Frequencies of crossovers and rearrangements in ERCC1⁺ and ERCC1^– cells with and without I-SceI treatment.

Cell line		Treatment	TK–APRT– cells (×10–6)a	Crossovers		Rearrangements
				Colonies	Frequency (×10–6)b	Colonies	Frequency (×10–6)b
AK784	ERCC1+	– I-SceI	2	16/16	2	0/16	<0.1
AK784	ERCC1+	+ I-SceI	2600 ± 1500	15/23	1700 ± 1070	8/23	900 ± 600
GSAK1	ERCC1–	– I-SceI	9.6 ± 1.5	3/20	1.4 ± 0.8	17/20	8.2 ± 2.4
GSAK1	ERCC1–	+ I-SceI	130 ± 69	10/22	59 ± 36	12/22	71 ± 43

^aValues are the means of the two experiments shown in Table 3. Standard errors of the means are indicated.

^bValues represent the frequency of TK^–APRT^– cells multiplied by the proportion of crossovers or rearrangements among the colonies analyzed. Standard rules for propagation of error were used to combine the standard error of the mean for TK^–APRT^– cells with the counting errors associated with the number of colonies counted in each class; the propagated errors are indicated.