PURIFICATION AND DNA-BINDING ACTIVITY OF THE PACA SUBUNIT OF THE BACTERIOPHAGE-P1 PACASE ENZYME

The bacteriophage P1 packaging site (pac) cleavage enzyme (pacase) con sists of two phage encoded proteins, PacA and PacB. Both proteins are necessary for the recognition and cleavage of pac and for subsequent p ackaging of cleaved DNA into phage particles. We have purified PacA to homogeneity from a bacterial strain that overproduces the protein. Pu rified PacA complements an Escherichia coli extract containing the Pac B protein for DNA cleavage at the pac site and recognizes and binds to methylated pac DNA independently of PacB in gel retardation experimen ts. The latter property of PacA is absolutely dependent on the presenc e of a wildtype E. coli extract, suggesting that E. coli host proteins play a role in the pac cleavage reaction.