Purification and crystallization of CII: An unstable transcription activator from phage lambda

The CII protein of the temperate bacteriophage lambda is a transcriptional activator involved in the lysis-lysogeny switch of the phage. It is an unst able protein of 97 amino acids and is known to exist as a tetramer in the n ative state. The cII gene has been cloned and expressed in Escherichia coli using a T7 promoter based over-expression system. The recombinant CII prot ein has been purified to homogeneity by ammonium sulfate fractionation foll owed by two steps of ion-exchange chromatography. The purified protein crys tallized at pH 8.2 in hanging-drop vapor diffusion method at 293 K. The cry stals diffract to a resolution of 2.8 Angstrom and belong to the space grou p C222 with unit-cell parameters a = 64.10, b = 106.95 and c = 120.16 Angst rom. (C) 2001 Academic Press.