[Bacteriophage P22 DNA structure in situ]

The structure of phage P22 DNA in situ was investigated by optical methods and by chemical modification with sodium bisulfite. On disruption of the phage particles by heating at 45 degrees a drop in absorbance at the 250 nm to 290 nm region was observed. At 260 nm this hypochromism was about 12%. CD spectra of intraphage DNA differed from that of free P22 DNA in the intensity as well as in the position of the positive band (lambda max 280 nm, delta epsilon max=1.3). In the intraphage DNA 21 per cent of cytosines reacted with sodium bisulfite. Cytosyl-amino acid products were found in the HClO4 and HCl hydrolysates of the modified phage. The main amino acid component of the product was identified as lysine. It was shown by means of gradient centrifugation and electron microscopy that the cytosyl-amino acid products result in the crosslinking of DNA to protein in the phage particles.