The NIT2 nitrogen regulatory protein of Neurospora: expression and stability of nit-2 mRNA and protein.

In Neurospora crassa, NIT2 is a global transcription factor that positively regulates the expression of up to 100 genes that are related to nitrogen metabolism. NIT2 is responsible for the lifting of nitrogen catabolite repression when the cellular levels of glutamine or other favored nitrogen sources become limited. Immunoprecipitation of the NIT2 protein showed that it is constitutively expressed, although its expression level is elevated a few-fold when nitrate instead of glutamine is used as the sole nitrogen source. The NIT2 protein is very stable and its stability is not affected by the nitrogen sources. The nit-2 transcripts appear to be very stable as well. The lack of significant regulation of cellular levels of nit-2 mRNA and of NIT2 protein suggests that its interactions with other proteins, e.g., in the nitrate assimilation pathway, with NIT4 and NMR, or post-translational modification of NIT2, may play important roles in modulating the function of NIT2 in response to environmental stimuli.