Crystallization and preliminary X-ray analysis of the C/EBPβ C-terminal region in complex with DNA

The C-terminal fragment (residues 259-345) of human C/EBPβ, a basic region leucine zipper transcriptional regulatory factor which includes the minimal DNA-binding domain, was crystallized in complex with a 16 bp DNA fragment from the tom-1 promoter. The crystals were in the form of a parallelepiped belonging to space group C222₁, had unit-cell parameters a = 100.7 (2), b = 113.5 (1), c = 74.4 (1) Å and diffracted to a resolution of 2.1 Å. Moreover, truncation of nine residues from the C-terminus not conserved among C/EBP family members yielded isomorphous crystals that diffracted to a resolution of 1.8 Å or better. Truncation of 14 residues from the N-terminus of the C-terminal fragment produced well shaped crystals in the form of hexagonal bipyramids, however; unfortunately, they were unstable and diffracted poorly.