[Ribonuclease Ap1 from Aspergillus pallidus. Purification, primary structure and crystallization].

Extracellular guanyl-specific RNAase of the fungus Aspergillus pallidus (RNAase ApI) was isolated in preparative amounts with a 40% yield and purified to homogeneity (938-fold). The complete amino acid sequence of the protein (104 amino acid residues) was determined: 6 Asp, 4 Asn, 4 Thr, 14 Ser, 3 Glu, 4 Gln, 4 Pro, 15 Gly, 9 Ala, 4 Cys, 6 Val, 2 Ile, 4 Leu, 10 Tyr, 4 Phe, 3 His, 4 Arg, 1 Trp. RNAase ApI has a molecular mass of 11,029 Da and is homologous to the family of fungal extracellular guanyl-specific RNAases. The primary structure of the protein is close to that of RNAase C2 from Asp. clavatus and differs from it by only 4 substitutions of amino acid residues. Monocrystals of RNAase ApI were grown which can be used for the X-ray analysis of proteins.