LASS4 is a member of the LASS (longevity assurance homologue) family which are involved in determining life span in yeast, by an unknown molecular mechanism. Members of this family are highly conserved from yeasts to mammals. Five mouse and human LASS family members, namely LASS1, LASS2, LASS4, LASS5 and LASS6, have been identified and characterized.
 
LASS proteins are thought to be involved in ceramide synthesis. Overproduction of a single LASS protein results in an increase in one or more specific ceramide species, which differ in fatty-acid chain length. LASS proteins possess specific fatty acyl-CoA preferences, but all can use sphingosine or dihydrosphingosine as the long-chain base substrate. LASS family members exhibit different tissue-specific expression patterns, which may contribute to the production of tissue-specific ceramides.