Purification, crystallization and preliminary X-ray analysis of the DNA-binding domain of AdpA, the central transcription factor in the A-factor regulatory cascade in the filamentous bacterium Streptomyces griseus, in complex with a duplex DNA

Streptomyces griseus AdpA is the central transcription factor in the A-factor regulatory cascade and activates a number of genes that are required for both secondary metabolism and morphological differentiation, leading to the onset of streptomycin biosynthesis as well as aerial mycelium formation and sporulation. The DNA-binding domain of AdpA consists of two helix-turn-helix DNA-binding motifs and shows low nucleotide-sequence specificity. To reveal the molecular basis of the low nucleotide-sequence specificity, an attempt was made to obtain cocrystals of the DNA-binding domain of AdpA and several kinds of duplex DNA. The best diffracting crystal was obtained using a 14-mer duplex DNA with two-nucleotide overhangs at the 5'-ends. The crystal diffracted X-rays to 2.8 Å resolution and belonged to space group C222₁, with unit-cell parameters a = 76.86, b = 100.96, c = 101.25 Å. The Matthews coefficient (V_M = 3.71 Å³ Da^-1) indicated that the crystal was most likely to contain one DNA-binding domain of AdpA and one duplex DNA in the asymmetric unit, with a solvent content of 66.8%.