Regulation of a Neurospora Crassa Extracellular RNase by Phosphorus, Nitrogen, and Carbon Derepressions

A new extracellular RNase, designated N4, was detected in culture filtrates from Neurospora crassa and its regulation was studied. Limitation of a nutrient obtainable from RNA alone was not sufficient to cause enzyme derepression. The addition of RNA to the medium had no inductive effect, but the addition of exogenous protein caused enzyme production. With protein in the medium, N4 was derepressible for all three elemental nutrients obtainable from RNA: carbon, nitrogen, and phosphorus. Successful carbon derepression required the addition of a small amount of proteolytic activity to the cultures, as has been reported for the carbon-derepressible proteases of N. crassa. Exogenous protein affected RNase production before translation. Effects of the exogenous protein appeared similar to those previously reported for N. crassa protease induction. N4 was under the control of the nit-2 and nuc-1 gene products. nit-2 and nuc-1 mutants were unable to derepress enzyme synthesis for nitrogen and phosphorus limitation, respectively; however, these mutants responded like wild types to the other two states of derepression. Enzyme synthesis was constitutive in the preg mutant. Results indicate that the transcription of the N4 structural gene responds to multiple regulatory gene products from different regulatory circuits and that external protein affects the synthesis of classes of hydrolases other than proteases.