"Aspergillus fumigatus" can survive on a variety of different nitrogen sources, and the assimilation of nitrogen is of clinical importance, as it has been shown to affect virulence. Proteins involved in nitrogen assimilation are transcriptionally regulated by the AfareA gene in "A. fumigatus". Targeted mutation of the afareA gene showed a decrease in onset of mortality in a mouse model of invasion. The Ras regulated protein RhbA has also been implicated in nitrogen assimilation. RhbA was found to be transcriptionally upregulated following contact of "A. fumigatus" with human endothelial cells, and strains with targeted mutation of the "rhbA "gene showed decreased growth on poor nitrogen sources and reduced virulence "in vivo".