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 m...