Dependence of transfection efficiency of calcium treated Escherichia coli cells on bacterial genotype and form of Lambda DNA.

The transfecting activity of linear lambda DNA is 100 times higher in calcium treated E. coli K12 (lambda i434) than in non-lysogenic strains: the levels of transfection are 1-2.10(7) and 1-2.10(5) infective centers per 1 mug of lambda DNA respectively. The high efficiency of lysogenic cells transfection is not due to the spontaneously liberated "helper" phage. Evidently, it is called forth by transfecting DNA-prophage recombination or/and by inhibition of nuclease activity in lysogenic cells. Both ring forms lambda DNA (supercoiled and open circles) show very low infectivity, if any, in calcinated cells.