Table 1. Effect of changes at HsdR Lys220 on the restriction phenotype of EcoR124I.

	Restriction activity a
HsdR	r− host b	r+ host c
WT	0.0025 ± 0.0026SD	0.00019 ± 0.000056
Lys220Arg	0.0014 ± 0.0014	0.00029 ± 0.000071
Lys220Ala	0.031 ± 0.0015	0.0012 ± 0.00028
Lys220Glu	0.27 ± 0.041	0.045 ± 0.034

^a Restriction activity was determined as the efficiency of plating of λvir.0 on the test strains relative to the efficiency of plating of λvir.0 on E. coli JM109(DE3) indicator (nonrestricting) strain as described in Methods. The values are the mean of at least three independent experiments. ^SD The standard deviation

^b Positive complementation was tested in r− host E. coli JM109(DE3)[pACMS] (r−m+).

^c Negative complementation was tested in r+ host E. coli JM109(DE3)[pKF650] (r+m+).