Transcription factor involved in the regulation of gene expression in response to extracellular amino acid levels. Synthesized as latent cytoplasmic precursor, which, upon a signal initiated by the plasma membrane SPS amino acid sensor system (including CSY1 and CSH3), becomes proteolytically activated and relocates to the nucleus, where it induces the expression of SPS-sensor-regulated genes. Required for efficient alkalinization through the release of ammonia from the cells produced during the breakdown of amino acids, and subsequent switch to the hyphal form. Localizes to the cytoplasm in its unprocessed form and is targeted to the nucleus after proteolytic processing upon induction by amino acids. Proteolytically cleaved: activated by the amino acid-induced proteolytic removal of an N-terminal inhibitory domain. Exhibits reduced capacity to take up amino acids and to switch to the hyphal form, and impairs response to farnesol.