Cloning, primary structure, and regulation of the HIS7 gene encoding a bifunctional glutamine amidotransferase: cyclase from Saccharomyces cerevisiae

Abstract

The Saccharomyces cerevisiae HIS7 gene was cloned by its location immediately downstream of the previously isolated and characterized ARO4 gene. The two genes have the same orientation with a distance of only 416 bp between the two open reading frames. The yeast HIS7 gene represents the first isolated eukaryotic gene encoding the enzymatic activities which catalyze the fifth and sixth step in histidine biosynthesis. The open reading frame of the HIS7 gene has a length of 1,656 bp resulting in a gene product of 552 amino acids with a calculated molecular weight of 61,082. Two findings implicate a bifunctional nature of the HIS7 gene product. First, the N-terminal and C-terminal segments of the deduced HIS7 amino acid sequence show significant homology to prokaryotic monofunctional glutamine amidotransferases and cyclases, respectively, involved in histidine biosynthesis. Second, the yeast HIS7 gene is able to suppress His auxotrophy of corresponding Escherichia coli hisH and hisF mutants. HIS7 gene expression is regulated by the general control system of amino acid biosynthesis. GCN4-dependent and GCN4-independent (basal) transcription use different initiator elements in the HIS7 promoter.

Imidazole Glycerol Phosphate Synthase fromThermotoga maritima

“…The products of this reaction, ImGP and 5-aminoimidazole-4-carboxamide ribotide (AICAR), are further used in histidine and de novo purine biosynthesis, respectively. In yeast, the glutaminase and synthase activities are located on a single polypeptide chain, which is termed HIS7 (12,13). The mechanism of glutamine hydrolysis by HisH can be deduced from the class I GATase carbamoyl phosphate synthase (5).…”

An Arabidopsis cDNA encoding a bifunctional glutamine amidotransferase/cyclase suppresses the histidine auxotrophy of a Saccharomyces cerevisiae his7 mutant

“…2. Alignment of the predicted amino acid sequences of Arabidopsis At-HF, S. cerevisiae HIS7 (accession number X69815) [11] and hisH, hisF gene products from E. coli (accession number X13462) [2], Synechocystis subsp. PCC6803 (accession numbers D64004, D90912) [25] and M. jannaschii (accession numbers U67493, U67500) [9].…”

“…2). In yeast S. cerevisiae, the glutamine amidotransferase (HisH) and the cyclase (HisF) domains are located at the Nterminal half and C-terminal half of a single polypeptide encoded by HIS7, respectively [11].…”

“…glutamine amidotransferase/cyclase An Arabidopsis expression sequence tag (EST) clone (186B18T7; GenBank accession number H37732) was identi¢ed as a putative cyclase (HisF) of Arabidopsis through the BLAST search against the Arabidopsis ESTs [16,17] with the aid of the primary structure deduced from the S. cerevisiae HIS7 gene [11]. In order to isolate fulllength cDNAs corresponding to the EST clone, total RNA was isolated from 7-day-old Arabidopsis seedlings by the acid guanidinium thiocyanate-phenol-chloroform extraction method [18], and a DNA fragment corresponding to the EST clone was ampli¢ed employing a reverse transcription (RT)-polymerase chain reaction (PCR) strategy.…”

“…Not only the overall gene organization but the structures of each gene are variable among di¡erent organisms. For example, in S. cerevisiae, HIS4 and HIS7 encode multifunctional enzymes [10,11]. The HIS7 gene of S. cerevisiae encodes the bifunctional glutamine amidotransferase (HisH) and the cyclase (HisF), although both proteins in eubacteria are encoded by independent cistrons, hisH and hisF, which are interrupted by the hisA cistron [2,12].…”