Component of the ceramide synthase complex that catalyzes the transfer of the acyl chain from acyl-CoA to a sphingoid base, with high selectivity toward hexacosanoyl-CoA (C26:0-CoA) (PubMed:12869556, PubMed:11694577). N-acylates sphinganine and phytosphingosine bases to form dihydroceramides and phytoceramides, respectively (PubMed:12869556). Redundant with LAC1. Facilitates ER-to-Golgi transport of GPI-anchored proteins. Involved in the aging process. Deletion of LAG1 results in a pronounced increase (approximately 50%) in mean and in maximum life span. a sphingoid base + a very long-chain fatty acyl-CoA = an N-(very-long-chain fatty acyl)-sphingoid base + CoA + H(+) hexacosanoyl-CoA + sphinganine = CoA + H(+) + N-hexacosanoylsphinganine sphinganine + tetracosanoyl-CoA = CoA + H(+) + N-tetracosanoylsphinganine eicosanoyl-CoA + sphinganine = CoA + H(+) + N-eicosanoylsphinganine a fatty acyl-CoA + sphinganine = an N-acylsphinganine + CoA + H(+) (4R)-hydroxysphinganine + a fatty acyl-CoA = an N-acyl-(4R)-4-hydroxysphinganine + CoA + H(+) Lipid metabolism; sphingolipid metabolism. Expression is controlled by CBF1. Belongs to the sphingosine N-acyltransferase family.