1. Department of Chemistry and Center for Molecular GeneticsUniversity of California at San DiegoLa JollaCalifornia92093USA
2. Laboratory of BiochemistryNational Heart, Lung, and Blood InstituteNational Institutes of HealthBethesdaMaryland20892USA
3. Schering‐Plough ResearchBloomfieldNew Jersey07003USA
4. Departments of Medicine and Cell BiologyDuke University Medical CenterDurhamNorth Carolina27710USA