TABLE 1.

Efficiency of homologous recombination in wild-type (mRad54^+/+ mRad54B^+/+), mRad54^−/−, mRad54B^−/−, and mRad54^−/− mRad54B^−/− ES cells as measured by homologous gene targeting^a

ES cell genotype	% of clones containing targeted locusb:
	mRad54	CTCF
mRad54+/+ mRad54B+/+	69.0 (87/126)	60.0 (54/90)
mRad54+/+ mRad54B−/−	64.7 (178/275)	54.0 (61/113)
mRad54−/− mRad54B+/+	2.1c (6/284)	21.3 (36/169)
mRad54−/− mRad54B−/−	<0.17 (0/560)	2.1 (7/332)

^aES cells of the indicated genotype were electroporated with the indicated gene targeting constructs. After selection under the appropriate conditions individual clones were isolated and expanded. Genomic DNA from the clones was isolated. For clones electroporated with the mRad54 targeting construct, genomic DNA was digested with the appropriate restriction enzyme, electrophoresed through an agarose gel, and transfered to a nylon membrane. Membranes were hybridized with radiolabeled probes that discriminated between homologously and randomly integrated targeting construct. For clones electroporated with the CTCF targeting construct, genomic DNA was used for PCRs that discriminated between random and homologous integration events.

^bThe percentage of clones containing the homologously integrated targeting construct relative to the total number of analyzed clones is indicated. Absolute numbers are indicated in parentheses. The differences in targeting efficiency between wild-type and mRad54^−/− cells, between wild-type and mRad54^−/− mRad54B^−/− cells, between mRad54^−/− and mRad54^−/−mRad54B^−/− cells, between mRad54B^−/− and mRad54^−/− cells, and between mRad54B^−/− and mRad54^−/− mRad54B^−/− cells are statistically significant for both loci (P < 0.001 by χ² analysis).

^cPreviously reported (34).