SUMMARY: The bacteriophage MAC-1, which specifically infects , was plaque purified and raised to high titre. The phage was purified by NaCl/polyethylene glycol precipitation, followed by two cycles of isopycnic density gradient centrifugation in CsCl. The purified phage exhibited a density of 1·363 g cm and a sedimentation coefficient of 94S. Nucleic acid isolated from purified phage was resistant to hydrolysis under alkaline conditions and to digestion with RNAase, but it was hydrolysed by DNAase, providing evidence that the phage genome is made up of DNA. The lack of hyperchromic effect upon denaturation, hydrolysis of phage DNA by SI nuclease, characteristic fluorescent staining with acridine orange, and resistance to digestion with a variety of restriction endonucleases are consistent with the DNA being single-stranded. A buoyant density of 1·722 g cm and a sedimentation coefficient of 17·9S were obtained for the phage DNA. The molecular mass of phage DNA was determined as 1·58 MDa by agarose gel electrophoresis with single-stranded DNA as standards. Electron microscopy of the DNA showed that the genome is circular in nature. In addition, using Southern blots, the two replicative forms, RFI (supercoiled)and RF2 (circular) have been identified and isolated from infected cell extracts.


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