Transcription factor required for repression of genes during iron starvation (PubMed:21062375). Represses iron-dependent and mitochondrial-localized activities including respiration, TCA cycle, amino acid metabolism, iron-sulfur-cluster and heme biosynthesis (PubMed:21062375). Iron starvation causes a massive remodeling of the amino acid pool and hapX is essential for the coordination of the production of siderophores and their precursor ornithine (PubMed:21062375). Expression is repressed by iron (PubMed:21062375). Expression is induced by the zinc cluster transcription factor acuM to stimulate expression of genes involved in both reductive iron assimilation and siderophore-mediated iron uptake (PubMed:20941352). Causes decreased production of triacetylfusarinine C (TAFC) but not fusarinine C (FsC) (PubMed:21062375). Attenuates virulence in a murine model of invasive aspergillosis (PubMed:21062375). Also increases zinc sensitivity (PubMed:21062375). Belongs to the bZIP family. YAP subfamily.