[1] Johns Hopkins Univ, Sch Med, Baltimore, MD 21205 USA
[2] Univ Oklahoma, Dept Chem & Biochem, Norman, OK 73019 USA
[3] Childrens Hosp Philadelphia, Div Human Genet & Mol Biol, Philadelphia, PA 19104 USA
[4] Wistar Inst Anat & Biol, Philadelphia, PA 19104 USA
[5] Torrey Pines Inst Mol Studies, San Diego, CA 92121 USA
[6] Univ New Mexico, Dept Biol, Albuquerque, NM 87131 USA