HAC1 / YFL031W Overview

Standard Name
HAC1 1
Systematic Name
ERN4 1 , IRE15 18
Feature Type
ORF , Verified
Basic leucine zipper (bZIP) transcription factor (ATF/CREB1 homolog); regulates unfolded protein response via UPRE binding and membrane biogenesis; translation initiation repressed under non-stress conditions by un-spliced intron that interacts with 5'-UTR; under ER stress Ire1p nuclease cleaves out inhibitory intron and triggers efficient Hac1p translation; two functional forms of Hac1p are produced; protein abundance increases in response to DNA replication stress 1 2 3 4 5 6 7 8 9 10 11 12 13
Name Description
Homologous to Atf/Creb1 5
Comparative Info
Sequence Details


The S. cerevisiae Reference Genome sequence is derived from laboratory strain S288C. Download DNA or protein sequence, view genomic context and coordinates. Click "Sequence Details" to view all sequence information for this locus, including that for other strains.

HAC1 is located in the middle of the left arm of chromosome VI between uncharacterized gene YFL032W and AGX1 alanine:glyoxylate aminotransferase; dubious ORF YFL031C-A overlaps the 3' end of HAC1 on the opposite strand; coding sequence is 969 nucleotides long with an intron at 662..913 and 10 SNPs, 2 of which cause amino acid polymorphisms
Protein Details


Basic sequence-derived (length, molecular weight, isoelectric point) and experimentally-determined (median abundance, median absolute deviation) protein information. Click "Protein Details" for further information about the protein such as half-life, abundance, domains, domains shared with other proteins, protein sequence retrieval for various strains, physico-chemical properties, protein modification sites, and external identifiers for the protein.

Hac1p is 238 amino acids long, low-to-moderate in abundance; contains basic-leucine zipper domain; phosphorylated on 6 residues; protein abundance increases in response to DNA replication stress
Length (a.a.)
Mol. Weight (Da)
Isoelectric Point
Median Abundance (molecules/cell)
5374 +/- 3596


Curated mutant alleles for the specified gene, listed alphabetically. Click on the allele name to open the allele page. Click "SGD search" to view all alleles in search results.

View all HAC1 alleles in SGD search

Gene Ontology Details

Gene Ontology

GO Annotations consist of four mandatory components: a gene product, a term from one of the three Gene Ontology (GO) controlled vocabularies (Molecular Function, Biological Process, and Cellular Component), a reference, and an evidence code. SGD has manually curated and high-throughput GO Annotations, both derived from the literature, as well as computational, or predicted, annotations. Click "Gene Ontology Details" to view all GO information and evidence for this locus as well as biological processes it shares with other genes.

Sequence-specific DNA-binding RNA polymerase II transcription factor involved in regulation of the unfolded protein response; also negatively regulates transcription during meiosis

View computational annotations

Molecular Function

Manually Curated

Cellular Component

Manually Curated
Phenotype Details


Phenotype annotations for a gene are curated single mutant phenotypes that require an observable (e.g., "cell shape"), a qualifier (e.g., "abnormal"), a mutant type (e.g., null), strain background, and a reference. In addition, annotations are classified as classical genetics or high-throughput (e.g., large scale survey, systematic mutation set). Whenever possible, allele information and additional details are provided. Click "Phenotype Details" to view all phenotype annotations and evidence for this locus as well as phenotypes it shares with other genes.

Non-essential gene; null mutants grow slowly, have decreased ethanol tolerance, are extremely sensitive to glycosylation inhibitor tunicamycin, show increased [PSI+] prion formation, are sensitive to Huntingtin, heat, zinc deficiency, and are auxotrophic for inositols; overexpression interferes with cell cycle progression and cytoskeleton morphology; heterozygous diploid nulls are haploinsufficient
Interaction Details


Interaction annotations are curated by BioGRID and include physical or genetic interactions observed between at least two genes. An interaction annotation is composed of the interaction type, name of the interactor, assay type (e.g., Two-Hybrid), annotation type (e.g., manual or high-throughput), and a reference, as well as other experimental details. Click "Interaction Details" to view all interaction annotations and evidence for this locus, including an interaction visualization.

Hac1p interacts physically with proteins involved in transcription; HAC1 interacts genetically with genes involved in lipid metabolism

940 total interactions for 471 unique genes

Physical Interactions

  • Affinity Capture-MS: 1
  • Affinity Capture-RNA: 59
  • Affinity Capture-Western: 2
  • Biochemical Activity: 2
  • Co-purification: 2
  • Protein-RNA: 8
  • Reconstituted Complex: 3
  • Two-hybrid: 4

Genetic Interactions

  • Dosage Lethality: 2
  • Dosage Rescue: 27
  • Negative Genetic: 569
  • Phenotypic Enhancement: 5
  • Phenotypic Suppression: 31
  • Positive Genetic: 90
  • Synthetic Growth Defect: 115
  • Synthetic Lethality: 9
  • Synthetic Rescue: 11
Regulation Details


The number of putative Regulators (genes that regulate it) and Targets (genes it regulates) for the given locus, based on experimental evidence. This evidence includes data generated through high-throughput techniques. Click "Regulation Details" to view all regulation annotations, shared GO enrichment among regulation Targets, and a regulator/target diagram for the locus.

HAC1 encodes a basic leucine zipper (bZIP) transcription factor of the ATF/CREB family that binds a 5'-RMCACGT-3' motif. Hac1p acts in coordination with Gcn4p to upregulate the unfolded protein response (UPR). The expression of ~380 genes is altered during the UPR, and roughly half have Hac1p binding sequences in the promoter. Hac1p induces the transcription of genes encoding both ER chaperones and components of the ER-associated degradation (ERAD) machinery, that contain one or more unfolded protein response elements (UPREs) in their promoters. UPR activation requires nonconventional splicing of the HAC1 mRNA in the cytoplasm. Unactivated HAC1 mRNA is constitutively expressed, but cannot be translated due to the presence of a 3' RNA hairpin. GTPase Ypt1p associates with and controls the RNA stability of unspliced HAC1 under normal growth conditions. Activated Ire1p cleaves the inactive HAC1 mRNA to remove the hairpin, which is then ligated by the Trl1p RNA ligase, allowing translation to proceed, and expression of Hac1p as a functional transcriptional activator. Hac1p then translocates to the nucleus and activates a large transcriptional program to compensate for the accumulation of misfolded proteins or other causes of ER stress.
Expression Details


Expression data are derived from records contained in the Gene Expression Omnibus (GEO), and are first log2 transformed and normalized. Referenced datasets may contain one or more condition(s), and as a result there may be a greater number of conditions than datasets represented in a single clickable histogram bar. The histogram division at 0.0 separates the down-regulated (green) conditions and datasets from those that are up-regulated (red). Click "Expression Details" to view all expression annotations and details for this locus, including a visualization of genes that share a similar expression pattern.

Summary Paragraph

A summary of the locus, written by SGD Biocurators following a thorough review of the literature. Links to gene names and curated GO terms are included within the Summary Paragraphs.

Last Updated: 2000-04-10

Literature Details


All manually curated literature for the specified gene, organized into topics according to their relevance to the gene (Primary Literature, Additional Literature, or Review). Click "Literature Details" to view all literature information for this locus, including shared literature between genes.