Purification and properties of the bacteriophage P2 ogr gene product: A prokaryotic zinc-binding transcriptional activator

The bacteriophage P2 ogr gene product, a 72-residue basic protein rich in cysteine and histidine, is a positive regulatory factor for phage late gene transcription in both P2 and satellite phage P4. We have developed a simple purification procedure for Ogr protein synthesized from an overproducing plasmid. Inclusion bodies formed upon overproduction were denatured using 8 M urea, and the overproduced protein was purified by gel filtration. The purified Ogr was allowed to refold under optimized conditions and was subsequently shown to be able to transactivate the phage P4 late promoter P_sid in an in vitro coupled transcription-translation system. Using a ⁶⁵Zn blotting method and absorption spectroscopy, we show that Ogr is a zinc-binding protein and that the conserved cysteine residues are involved in forming a complex with Zn(II). The purification procedure described allows Ogr to be obtained in both high purity and yield.