Table 2. λ Red recombination efficiency with dsDNA with ssDNA overhangs.

	Prophage			Recombinants†
Strain*	exo	bet	gam	3′ overhangs‡	5′ overhangs‡
DY411	+	+	+	3.0 × 102	1.4 × 105
DY418	+	+	-	4.0 × 101	2.0 × 104
DY419	+	-	+	<1	<1
DY420	-	+	+	2.0 × 102	1.2 × 102
DY433	-	+	-	3.0 × 101	3.8 × 102

^*Besides the prophage genotype listed, all strains contain a 34-bp deletion in galK replaced by Km^r. The cat substitution mutations in exo, bet, and gam were constructed as described (2). The Red-induced cells made from these strains were electroporated with ≈100 ng of each oligo

^†Recombinant and viable cells were normalized and determined as in Table 1. Values for 3′ and 5′ overhangs in DY411 are the average of 12 and 21 experiments, respectively. Absolute values in experiments vary up to 4-fold from the mean. This variation holds in all other experiments reported. On a given day, however, all experiments yield more internally consistent values than values compared between days

^‡Oligos used for 3′ overhangs were 37/106 and -70/-1. Oligos used for 5′ overhangs were 1/70 and -106/-37 as shown in Fig. 2