title: The Saccharomyces cerevisiae LSB6 gene encodes phosphatidylinositol 4-kinase activity.
abstract: The LSB6 gene product was identified from the Saccharomyces Genome Data Base (locus YJL100W) as a putative member of a novel type II phosphatidylinositol (PI) 4-kinase family. Cell extracts lacking the LSB6 gene had a reduced level of PI 4-kinase activity. In addition, multicopy plasmids containing the LSB6 gene directed the overexpression of PI 4-kinase activity in cell extracts of wild-type cells, in an lsb6Delta mutant, in a pik1(ts) stt4(ts) double mutant, and in an pik1(ts) stt4(ts) lsb6Delta triple mutant. The heterologous expression of the S. cerevisiae LSB6 gene in Escherichia coli resulted in the expression of a protein that possessed PI 4-kinase activity. Although the lsb6Delta mutant did not exhibit a growth phenotype and failed to exhibit a defect in phosphoinositide synthesis in vivo, the overexpression of the LSB6 gene could partially suppress the lethal phenotype of an stt4Delta mutant defective in the type III STT4-encoded PI 4-kinase indicating that Lsb6p functions as a PI 4-kinase in vivo. Lsb6p was localized to the membrane fraction of the cell, and when overexpressed, GFP-tagged Lsb6p was observed on both the plasma membrane and the vacuole membrane. The enzymological properties (pH optimum, dependence on magnesium or manganese as a cofactor, the dependence of activity on Triton X-100, the dependence on the PI surface concentration, and temperature sensitivity) of the LSB6-encoded enzyme were very similar to the membrane-associated 55-kDa PI 4-kinase previously purified from S. cerevisiae.
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase / Q000737:chemistry / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D002455:Cell Division; D004247:DNA / Q000378:metabolism; D019992:Databases as Topic; D003902:Detergents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007425:Intracellular Membranes / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D009154:Mutation; D017830:Octoxynol / Q000494:pharmacology; D010641:Phenotype; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D013347:Subcellular Fractions / Q000378:metabolism; D013696:Temperature; D014617:Vacuoles / Q000378:metabolism
chemical_list: D003902:Detergents; D008345:Manganese; D012965:Sodium Chloride; D000255:Adenosine Triphosphate; D017830:Octoxynol; D004247:DNA; D019870:1-Phosphatidylinositol 4-Kinase; D008274:Magnesium