Phosphate Medium

The production of ribonucleic acid (RNA)-depolymerase-forming 5'-nucleotides (5'-nuclease) was investigated with the fungus Aspergillus quercinus in media containing 68, 10, 5, 3, 1, and 0.5 mg of phosphorus per 100 ml. Yields were maximal with 5 mg of phosphorus per 100 ml. RNA-depolymerase-forming 3'-nucleosides (3'nuclease) and phosphomonoesterase were maximal in media containing 1 and 0.5 mg of phosphorus per 100 ml. The 5'-nuclease was purified approximately 530-fold with a recovery of 84% by column chromatography on diethylaminoethyl-cellulose and by gel filtration through Sephadex G-100. The purified enzyme was capable of acting on both deoxyribonucleic acid and RNA, and the 5'-mononucleotides produced were identified by paper chromatography. The enzyme 5'-nuclease appears to be one of the repressible exonucleases that are active in the production of 5'-mononucleotides.