Sphingosine-1-phosphate (SPP) participates in the proliferative signal transduction pathways of mammalian cells. SPP synthesis is catalyzed by sphingosine kinase, and SPP degradation is catalyzed by SPP lyase (SPL). The first SPL gene cloned, BST1 ('bestowed of sphingosine tolerance'), was isolated from budding yeast . A yeast mutant strain containing a deletion of the entire BST1 coding region is sensitive to the growth-inhibitory effects of D-erythro-sphingosine, due to its inability to degrade SPP. Spl, that has 59% sequence similarity to the BST1 gene product. They showed that this cDNA can functionally complement the yeast BST1 deletion, restoring a sphingosine-resistant phenotype. Northern blot analysis detected Spl expression in several mouse tissues, with the highest level found in the liver.