Crystallization and preliminary X-ray diffraction analysis of KsgA, a universally conserved RNA adenine dimethyltransferase in Escherichia coli.

The bacterial enzyme KsgA catalyzes the transfer of a total of four methyl groups from S-adenosylmethionine (SAM) to two adjacent adenosines in 16S rRNA. These modified adenosines are universally conserved in all species of eubacteria, eukaryotes and archaebacteria studied. Recombinant KsgA from Escherichia coli was overexpressed as a His-tagged fusion protein and purified. The recombinant protein was crystallized using PEG 4000 as a precipitant. The crystals belong to space group C2 and diffract X-rays to a resolution of 1.9 A. The unit-cell parameters are a = 173.9, b = 38.4, c = 83.0 A, beta = 90.0 degrees. Structure determination using the molecular-replacement method is at the early stages of refinement.