Nuclease Rsn from Rhizopus stolonifer catalyzes the hydrolysis of ss-and dsDNA in a ratio of approximately 2:1. Time course of 3' and 5' terminal analysis of the hydrolytic products of ss- and dsDNA showed that nuclease Rsn does not show any strict base preference and cleaves DNA in a non-specific manner. Moreover, separation of the hydrolytic products of ss- and dsDNA in the presence of Mg2+, Mn2- or Co2+ showed the predominance of tetra-, tri-, and dinucleotides followed by mononucleotides, suggesting an endo mode of action. (C) 2004 Elsevier Inc. All rights reserved.