TABLE 1.

Positive selection by EcoK restriction^a

Expt	cDNA-positive coloniesb		Selection factorc
	E. coli M15	E. coli TG1
1	0.78	0.05	15.6
2	0.84	0.06	15.2

^acDNA-containing colonies after transformation of two different E. coli strains were detected by PCR analysis. Typical results of two independent experiments are shown. 

^bRelative numbers of cDNA-positive colonies in relation to total numbers of randomly analyzed colonies. 

^cSelection factors were calculated as the ratio of values for EcoK-positive (M15) and EcoK-negative (TG1) E. coli strains.