title: Expression of 1L-myoinositol-1-phosphate synthase in organelles.
abstract: We have studied the expression of 1L-myoinositol-1-phosphate synthase (MIPS; EC 5.5.1.4) in developing organs of Phaseolus vulgaris to define genetic controls that spatially regulate inositol phosphate biosynthesis. MIPS, the pivotal biosynthetic enzyme in inositol metabolism, is the only enzyme known to catalyze the conversion of glucose 6-phosphate to inositol phosphate. It is found in unicellular and multicellular eukaryotes and has been isolated as a soluble enzyme from both. Thus, it is widely accepted that inositol phosphate biosynthesis is largely restricted to the cytosol. Here, we report findings that suggest the enzyme is also expressed in membrane-bound organelles. Microscopic and biochemical analyses detected MIPS expression in plasma membranes, plastids, mitochondria, endoplasmic reticula, nuclei, and cell walls of bean. To address mechanisms by which the enzyme could be targeted to or through membranes, MIPS genes were analyzed for sorting signals within primary structures and upstream open reading frames that we discovered through our sequence analyses. Comprehensive computer analyses revealed putative transit peptides that are predicted to target the enzyme to different cellular compartments. Reverse transcriptase PCR experiments suggest that these putative targeting peptides are expressed in bean roots and leaves.
authors.affiliation: Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama 35487, USA.
authors.forename: Kimberly Helms
authors.initials: KH
authors.lastname: Lackey
authors.forename: Patricia Marie
authors.initials: PM
authors.lastname: Pope
authors.forename: Margaret Dean
authors.initials: MD
authors.lastname: Johnson
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002458:Cell Fractionation; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D015151:Immunoblotting; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D015388:Organelles / Q000201:enzymology*; D027805:Phaseolus / Q000166:cytology* / Q000201:enzymology* / Q000235:genetics; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012995:Solubility
chemical_list: D007527:Isoenzymes; D012333:RNA, Messenger; D010744:Phosphoric Monoester Hydrolases; C021822:myo-inositol-1 (or 4)-monophosphatase