Nitrate assimilation in the fungus Neurospora, particularly the steps connected with nitrite assimilation and reduction to ammonium ion, is the object(s) of the proposed research. An analysis of the sequence organization and regulated expression of the nitrite reductase structural gene, "nit-6", and a comparison of its properties with those of "nit-3", its coordinately regulated partner, is an immediate goal of the research. The information obtained will be exploited in experiments designed to probe structure:activity relationships in nitrite reductase.