Coetzee, Smit & Prozesky (1966) described three serologically related phages PL25, PL26 and PL37 which produce generalized transduction in the hosts. It was decided to investigate the physical properties of the nucleic acid of phage PL25 because this phage could usually be prepared in higher titre than its relatives.

Crude lysates (5 × 10 p.f.u./ml.) were partially purified by differential centrifugation. Pellets were resuspended in saline-citrate buffer (0.15 -NaCl + 0.015 -citrate) at pH 7.0 to a titre of about 5 × 10 p.f.u./ml. Phage DNA was prepared by the method of Mandell & Hershey (1960). The presence and concentration of DNA were determined by the diphenylamine reaction (Kupila, Bryan & Stern, 1961) and ultraviolet absorption at 260 nm. (1 µg. DNA/ml. = 0.0205 absorbency units). Concentrations of DNA ranged from 400 to 600 µg./ml. and no protein was detected by the Lowry procedure (Lowry 1951).


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