text: X-ray crystallography is a technique that measures the angles and intensities of crystalline atoms in order to determine the atomic and molecular structure of the crystal of interest.  Crystallographers are then able to produce and three-dimensional picture where the positions of the atoms, chemical bonds as well as other important characteristics can be determined. Klimasaukas and colleagues used this technique to observe the first base flipping phenomenon, in which their experimental procedure involved several steps: 
  # Purification
  # Crystallization
  # Data Collection
  # Structure determination and refinement
  During purification, Haemophilus haemolyticus methyltransferase was overexpressed and purified using a high salt back-extraction step to selectively solubilize M.HhaI, followed by fast protein liquid chromatography (FPLC) as done previously by Kumar and colleagues. Authors utilized a Mono-Q anion exchange column to remove the small quantity of proteinaceous materials and unwanted DNA prior to the crystallization step. Once M.HhaI was successfully purified, the sample was then grown using a method that mixes the solution containing the complex at a temperature of 16 °C and the hanging-drop vapor diffusion technique to obtain the crystals. Authors were then able to collect the x-ray data according to a technique used by Cheng and colleagues in 1993. This technique involved the measurement of the diffraction intensities on a FAST detector, where the exposure times for 0.1° rotation were 5 or 10 seconds. For the structure determination and refinement, Klimasaukas and colleagues used the molecular replacement of the refined apo structure described by Cheng and colleagues in 1993 where the search models  X-PLOR, MERLOT, and TRNSUM were used to solve the rotation and translation functions. This part of the study involves the use of a variety of software and computer algorithms to solve the structures and characteristics of the crystal of interest.