Transfection of Escherichia coli spheroplasts. I. General facilitation of double-stranded deoxyribonucleic acid infectivity by protamine sulfate.

The addition of 25 mug of protamine sulfate per ml to lysozyme-ethylenediamine-tetraacetic acid spheroplasts of Escherichia coli stimulates transfection not only for T1 phage deoxyribonucleic acid (DNA; Hotz and Mauser, 1969) but also for the following phage DNA species: lambda, 10,000-fold to an efficiency of 10(-3) infective centers per DNA molecule; phiX174 replicative form, 300-fold to an efficiency of 5 x 10(-2); fd replicative form, 300-fold to 10(-6); T7, 300-fold to 3 x 10(-7). Three native phage DNA species were not infective at all in the absence of protamine sulfate but were infective in the presence of protamine sulfate with the following efficiencies: T4, 10(-5); T5, 3 x 10(-6); and P22, 3 x 10(-9). The effect of protamine sulfate is specific for double-stranded DNA. The application of infectivity assays to the study of phage DNA replication, recombination, prophage integration, prophage excision, and interspecies transfection are discussed.