Purification and crystallization of Phd, the antitoxin of the phd/doc operon

The antitoxin Phd from the phd/doc module of bacteriophage P1 was crystallized in two distinct crystal forms. Crystals of His-tagged Phd contain a C-terminally truncated version of the protein and diffract to 2.20 Å resolution. Crystals of untagged Phd purified from the Phd-Doc complex diffract to 2.25 Å resolution. These crystals are partially merohedrally twinned and contain the full-length version of the protein.