Disease relevance of INO2

• By the use of size variants and by heterologous expression in E. coli we demonstrate that Ino2p and Ino4p are both necessary and sufficient for the formation of the previously described FAS binding factor 1, Fbf1, interacting with the ICRE [1].

High impact information on INO2

• These data suggest that the OPI1 gene product is the primary target (sensor) of the inositol response and that derepression of INO2 transcription determines the degree of expression of the target genes [2].
• The expression of the INO1 and CHO1 target genes was still responsive to inositol even though expression of the INO2 gene was unresponsive [2].
• However, the level of expression of the INO1 and CHO1 target genes correlated with the level of INO2 transcription [2].
• We investigated these possibilities by examining the effect of inositol on target gene expression in a strain containing the INO2 gene under control of the GAL1 promoter [2].
• Using a cat reporter gene, we find that INO2-cat expression was regulated 12-fold in response to inositol and choline but that INO4-cat was constitutively expressed [3].

Biological context of INO2

• Our data show that derepression of phospholipid biosynthetic gene expression involves two mechanisms: increasing the levels of the INO2 and INO4 gene products and inactivating the OPI1-mediated repression mechanism [3].
• The INO2 open reading frame codes for a 304 amino acid protein with a calculated molecular weight of 39.7 kDa [4].
• Mutant strains in which the INO2 chromosomal locus has been deleted show pleiotropic phenotypes under growth conditions of inositol/choline availability [4].
• Furthermore, a disruption of APL2 together with INO2 or INO4 rendered yeast cells sensitive to oxidative stress [5].
• Removal of inositol results in transcriptional activation by heterodimeric complexes of two bHLH proteins, Ino2p and Ino4p [6].

Anatomical context of INO2

• Many ino2 delta cells show delocalized cell growth resulting in large cells having aberrant shapes [4].
• Of these, the INO2 gene product was found to be essential for formation of p180-inducible membranes [7].

Associations of INO2 with chemical compounds

• In the absence of inositol and choline (derepressing), the products of the INO2 and INO4 genes form a heteromeric complex which binds to a 10-bp element, upstream activation sequence INO (UASINO), in the promoters of the phospholipid biosynthetic genes to activate their transcription [3].
• The INO4 and INO2 genes were, thus, previously identified as regulatory genes whose wild-type product is required for expression of the INO1 gene product inositol-1-phosphate synthase (T. Donahue and S. Henry, J. Biol. Chem. 256:7077-7085, 1981) [8].
• INO2-APL2 double disruptants also showed growth inability in non-fermentable carbon sources, such as glycerol [5].
• In addition to the identification of a new ino4-allele, further characterization of the existing series of ino4 and ino2 mutants, reported here, demonstrated that they all have a reduced capacity to convert phosphatidylethanolamine to phosphatidylcholine [8].
• By alanine scanning mutagenesis of the entire RID we were able to identify nine residues critical for Opi1-dependent repression of Ino2 function [9].

Physical interactions of INO2

• UAS(ADR1) is a presumed binding site for the zinc finger transcription factor Adr1p and UAS(INO) is a presumed binding site for the basic helix-loop-helix transcription factors Ino2p and Ino4p [10].
• Yeast transcriptional activator INO2 interacts as an Ino2p/Ino4p basic helix-loop-helix heteromeric complex with the inositol/choline-responsive element necessary for expression of phospholipid biosynthetic genes in Saccharomyces cerevisiae [1].
• Ino2p-dependent binding activity overlapped with a region of the INO1 promoter that contains two potential HLH consensus binding sites [11].
• Results of an in vitro assay have led to a model in which Opi1p interacts with Ino2p [12].
• Ino2 interacts physically with the basal transcription factor Sua7 (TFIIB of yeast) [13].

Regulatory relationships of INO2

• CDS1 expression is repressed in concert with INO2 expression in response to inositol [14].
• This suggests that Ume6p does not regulate INO2 expression indirectly by regulating OPI1 expression [15].
• We have shown previously that the UME6 gene positively regulates INO2 expression [16].

Other interactions of INO2

• Curiously, we identified a UASINO-like element in the promoters of both the INO2 and INO4 genes [3].
• This factor is not functionally identical to Ino2p since other inositol-responsive genes (e.g. CHO1 ) maintain INO2 -dependent expression in nmt1-451D cells [6].
• FAS1 expression is Ino2p-dependent in NMT1 cells at 24-33 degreesC [6].
• In contrast, FAS1 expression becomes Ino2p-independent in nmt1-451D cells at temperatures where efficient acylation of cellular N-myristoylproteins is jeopardized [6].
• We have independently identified and DNA sequenced the INO2 locus by its close proximity to the KIN1 locus in Saccharomyces cerevisiae [4].

Analytical, diagnostic and therapeutic context of INO2

• Northern blot analysis revealed that two of these three genes, designated as DIE1 and DIE2, clearly increased the expression of ITR1 [17].
• Immunoprecipitation experiments demonstrate that Ino2p and Ino4p interact in the absence of DNA [18].

References