Infection of protoplasts and spheroplasts by isolated bacteriophage DNA with production of whole phage has been reported for a number of organisms (Riggs & Rosenblum, 1969). This phenomenon has not previously been described in strains.

DNA was prepared from phage 13 (Prozesky, de Klerk & Coetzee, 1965) by the technique of Gierer & Schramm (1956). The concentration of DNA, determined by optical extinction at 260 nm. (1 µg. DNA/ml. = 0.0205 absorbency units), ranged from 200 to 600 µg./ml. Sedimentation coefficients of the DNA at concentrations of 10 to 50 µg./ml. were determined in a Spinco model E ultracentrifuge (Rosenblum & Schumaker, 1963). The DNA was homogeneous and an average molecular weight of 26.3 × 10 was calculated. Sedimentation of the DNA through an alkaline sucrose gradient revealed no single-strand breaks.


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