Crystallization and prelilminary X‐ray investigation of barster, the intracellular inhibitor of barnase

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Abstract
Crystals of barstar, the intracellular inhibitor of the extracellular ribonuclease produced by Bacillus amyloliquefaciens (barnase), were obtained through vapor phase equilibration using the hanging drop technique. Three crystal forms have been characterized. Forms I and II, crystallized eithr in potetragonal; they exhibit a superstructure along the c-axis. Form III crystals, suitable for a high resolution structure determination, were grown from 55-65% ammomnium sulfate. This crystal form is hexagonal and diffracts to at least 2 Å resolution at a synchrotron radiation source. It belongs to the hexagonal space group P6, with unit cell dimensions a = b = 143.6 Å, c = 35.6 Å. There are four molecules of barstar in the asymmetric unit. X-ray data have been collected to 2.2 Å Bragg sapcing. The structure determination is underway in order to analyze conformational changes of barstar upon complexation with barnas.