Structure and synthesis of a lipid-containing bacteriophage. Dissociation of bacteriophage PM2 into its morphological subunits.

The lipid-containing bacteriophage PM2 was dissociated stepwise in 1 M NcCl (pH 7.2)with increasing urea concentrations. In 2 M urea the following substructures could be identified: (a) a nucleocapsid containing all of the viral lipid, the DNA, proteins III and IV, plus a fraction of protein II, and (b) a second substructure respresenting particles which contained all viral elements except protein I, the spike protein. In 4 M urea the viral nucleocapsid containing all of proteins III and IV, the DNA, plus a fraction of protein II, was isolated. Upon increasing the urea concentration further, this nucleocapsid is stable up to 8.5 M urea; in 9 M urea protein III was partly dissociated from the nucleocapsid. The nucleocapsid in 4--8.5 M urea is stabilized by the addition of 0.1--3 M NaCl but dissociates if the NaCl concentration is less than 0.1 M. The nucleocapsid was also dissociated in 4--8.5 M urea at pH 4.5. The nucleocapsid structures and some intermediate morphological subunits have been analysed by physical methods, enabling us to draw some conclusions about the structure and hydration of the virus.