Regulation of hisHF transcription of Aspergillus nidulans by adenine and amino acid limitation

The hisHF gene of Aspergillus nidulans encodes imidazole-glycerole-phosphat e (IGP) synthase, consisting of a glutamine amidotransferase and a cyclase domain. The enzyme catalyzes the fifth and sixth steps of histidine biosynt hesis, which results in an intermediate of the amino acid and an additional intermediate of purine biosynthesis, An A. nidulans hisHF cDNA complemente d a Saccharomyces cerevisiae his7 Delta strain and Escherichia coil hisH an d hisF mutant strains, The genomic DNA encoding the hisHF gene was cloned a nd its sequence revealed two introns within the 1659-bp-long open reading f rame. The transcription of the hisHF gene of A, nidulans is activated upon amino acid starvation, suggesting that hisHF is a target gene of cross path way control, Adenine but not histidine, both end products of the biosynthet ic pathways connected by the IGP synthase, represses hisHF transcription, I n contrast to other organisms HISHF overproduction did not result in any de velopmental phenotype of the fungus in hyphal growth or the asexual life cy cle, hisHF overexpression caused a significantly reduced osmotic tolerance and the inability to undergo the sexual life cycle leading to acleistotheci al colonies. (C) 2001 Academic Press.