Nature 410, 596–599; 2000

In the second paragraph of this paper, (trans-4-sphingenine, d18:1 (ref. 4)) should have read (trans-4-sphingenine, d18:14); (d18:1 (ref. 8)) should have read (d18:18); (d18:2 (refs 4,8)) should have read (d18:24,8); and (t18:1 (ref. 10)) should have read (t18:18)10.