Disease relevance of INO4

• Computer analysis of the INO4 protein sequence identified several potential phosphorylation sites as well as several regions that contained significant similarities with the lupus LA antigen and with the helix-loop-helix region of the Myc family of proteins [1].
• 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 [2].

High impact information on INO4

• 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].
• Cells bearing the ino2 or ino4 regulatory mutations, which exhibit constitutively repressed levels of a number of phospholipid biosynthetic enzymes, had constitutively repressed levels of 1.2-kb RNA and PSS activity [4].
• The ino2 and ino4 mutants, originally isolated on the basis of an inositol requirement, are unable to derepress the cytoplasmic enzyme inositol-1-phosphate synthase (myo-inositol-1-phosphate synthase; EC 5.5.1.4) [5].
• It was also found to be auxotrophic for inositol and allelic to an existing series of ino4 mutants [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 [5].

Biological context of INO4

• Furthermore, a disruption of APL2 together with INO2 or INO4 rendered yeast cells sensitive to oxidative stress [6].
• Removal of inositol results in transcriptional activation by heterodimeric complexes of two bHLH proteins, Ino2p and Ino4p [7].
• The ino4-8 mutation is a single base pair change that results in substitution of lysine for glutamic acid at position 79 in the bHLH domain of the yeast regulatory protein, Ino4p [8].
• Translation of the DNA sequence of the INO4 gene results in a very basic protein of molecular weight 17,378 [1].
• The INO4 gene has been mapped to chromosome 15 and is tightly linked to the SUF1 tRNA gene [1].

Anatomical context of INO4

• Thus, Ino2p is required for the formation of p180-induced membranes and, in this case, appears to be functional in the absence of its putative binding partner, Ino4p [9].

Associations of INO4 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].
• Mutations at the INO4 locus result in a decrease in phosphatidylcholine synthesis and an inability to derepress the structural genes for inositol-1-phosphate synthase and phosphatidylserine synthase [1].

Physical interactions of INO4

• Ino2p and Ino4p bind to Apl2p independently, but more strongly when both are present [6].
• 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 [2].

Other interactions of INO4

• Three previously identified genes that regulate general phospholipid synthesis, INO2, INO4, and OP11, did not affect PGPS expression [10].
• We tested the hypothesis that N-myristoylproteins function to regulate INO2, INO4 and/or OPI1 transcription, thereby affecting the expression of inositol-sensitive genes that influence myristoylCoA metabolism [7].
• Ino4p dimerizes with a second bHLH protein, Ino2p, to form a complex that binds to the promoter of the INO1 gene, activating transcription [8].
• We demonstrate in vitro binding of the heterodimeric activator protein Ino2p/Ino4p to the ACS2 promoter [11].
• We found that Ino2p, Ino4p, and Apl2p form a ternary complex [6].

Analytical, diagnostic and therapeutic context of INO4

• Immunoprecipitation experiments demonstrate that Ino2p and Ino4p interact in the absence of DNA [12].
• In gel retardation assays, the protein-DNA complex involving the previously described FAS binding factor 1, Fbf1, was absent when using a protein extract from the delta ino4 mutant [13].

References