THE LCB4 (YOR171C) AND LCB5 (YLR260W) GENES OF SACCHAROMYCES ENCODE SPHINGOID LONG-CHAIN BASE KINASES

Sphingolipid long chain bases (LCBs) and phosphorylated derivatives, p articularly sphingosine l-phosphate, are putative signaling molecules. To help elucidate the physiological roles of LCB phosphates, we ident ified two Saccharomyces cerevisiae genes, LCB4 (YOR171c) and LCB5 (YLR 260w), which encode LCB kinase activity. This conclusion is based upon the synthesis of LCB kinase activity in Escherichia coli expressing e ither LCB gene. LCB4 encodes most (97%) Saccharomyces LCB kinase activ ity, with the remainder requiring LCB5. Log phase Icb4-deleted yeast c ells make no LCB phosphates, showing that the Lcb4 kinase synthesizes all detectable LCB phosphates under these growth conditions. The Lcb4 and Lcb5 proteins are paralogs with 53% amino acid identity but are no t related to any known protein, thus revealing a new class of lipid ki nase, Two-thirds of the Lcb4 and one-third of the Lcb5 kinase activity are in the membrane fraction of yeast cells, a puzzling finding in th at neither protein contains a membrane-localization signal. Both enzym es can use phytosphingosine, dihydrosphingosine, or sphingosine as sub strate. LCB4 and LCBB should be useful for probing the functions of LC B phosphates in S. cerevisiae, Potential mammalian cDNA homologs of th e LCB kinase genes may prove useful in helping to understand the funct ion of sphingosine l-phosphate in mammals.