Hoshizaki D K, Hill J E, Henry S A
Department of Biological Chemistry, College of Medicine, University of Illinois, Chicago 60612.
J Biol Chem. 1990 Mar 15;265(8):4736-45.
The INO4 gene product is believed to be a positive regulatory factor in a complex cascade of positive and negative factors that coordinates the synthesis of phospholipids in the yeast Saccharomyces cerevisiae. 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. In the present study, the transcript encoding the INO4 gene product has been identified and a transcription map of the INO4 region has been constructed. An ino4 deletion mutant was constructed by in vitro gene disruption and the deletion mutant was shown to be viable but auxotrophic for inositol. The deletion mutant expressed repressed levels of inositol-1-phosphate synthase (INO1) mRNA and exhibited reduced phosphatidylcholine biosynthesis, a phenotype similar to previously characterized ino4 mutants. The INO4 gene has been mapped to chromosome 15 and is tightly linked to the SUF1 tRNA gene. Translation of the DNA sequence of the INO4 gene results in a very basic protein of molecular weight 17,378. 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.
INO4基因产物被认为是一种正调控因子，参与酿酒酵母中磷脂合成的正负因子复杂级联反应。INO4位点的突变导致磷脂酰胆碱合成减少，且无法解除对肌醇-1-磷酸合酶和磷脂酰丝氨酸合酶结构基因的阻遏。在本研究中，已鉴定出编码INO4基因产物的转录本，并构建了INO4区域的转录图谱。通过体外基因破坏构建了ino4缺失突变体，该缺失突变体被证明是有活力的，但对肌醇营养缺陷。该缺失突变体表达受抑制水平的肌醇-1-磷酸合酶（INO1）mRNA，且磷脂酰胆碱生物合成减少，其表型与先前鉴定的ino4突变体相似。INO4基因已定位到15号染色体，且与SUF1 tRNA基因紧密连锁。INO4基因的DNA序列翻译产生一种分子量为17378的碱性很强的蛋白质。对INO4蛋白序列的计算机分析确定了几个潜在的磷酸化位点，以及几个与狼疮LA抗原和Myc蛋白家族的螺旋-环-螺旋区域有显著相似性的区域。
