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.
SciCrunch is a data sharing and display platform. Anyone can create a custom portal where they can select searchable subsets of hundreds of data sources, brand their web pages and create their community. SciCrunch will push data updates automatically to all portals on a weekly basis. User communities can also add their own data to scicrunch, however this is not currently a free service.