PURIFICATION AND PROPERTIES OF PROTEINS ESSENTIAL TO DNA ENCAPSULATION BY PHAGE-P22

Two noncapsid P22 proteins, p2 and p3, are required for DNA encapsulation. In the in vitro encapsulation system described in the preceding paper, DNA donor extracts lacking p2 or p3 due to mutation are defective. Reconstitution of a 2- DNA donor extract by an exogenous source of p2 serves as an assay for p2 activity. Attempts to reconstitute 3- DNA donor extracts have not been successful. p2 can be purified from 3--infected cells. The purified active material sediments as an apparent monomer. When the source of p2 is 3+-infected cells, p2 activity resides in an apparent p2-p3 complex that sediments substantially gaster than monomer p2. p2 activity is unstable in the absence of ATP. These results suggest that p2 and p3 normally function as a complex that interacts with ATP, DNA and proheads in the encapsulation process. © 1979.