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RNase Sa2 (97 amino-acid residues, MW = 10 894 Da) is an extracellular ribonuclease isolated from Streptomyces, aureofaciens, strain R8/26. The enzyme hydrolyses the phosphodiester bond of RNA at the 3'-side of guanosine nucleotides. Two crystal forms of RNase Sa2/3'-GMP complex were obtained. Crystal form I was prepared by diffusion of mononucleotide into the pre-grown crystals of RNase Sa2. Crystal form II was obtained by re-crystallization of RNase Sa2 with 3'-GMP. Both crystal forms belong to space group C(2). The crystals diffracted to 2.2 and 2.25 Angstrom, respectively. Unit cell parameters for crystal form I and II are: a = 101.52, b = 65.90, c = 56:96 Angstrom, beta = 100.92degrees, and a = 108.20, b = 62.65, c = 68.30 Angstrom, beta = 129.80degrees, respectively. The V(M) values are 2.86 and 2.04 Angstrom(3) Da(-1), respectively.. The crystal form I contains three and the crystal form II four …