[1] Clemson Univ, Dept Genet & Biochem, S Carolina Expt Stn, Clemson, SC 29634 USA
[2] MIT, Biol Engn Div, Cambridge, MA 02139 USA
[3] Univ Texas Galveston, Med Branch, Scaly Ctr Mol Sci & Biochem, Galveston, TX 77555 USA
[4] Univ Texas Galveston, Med Branch, Scaly Ctr Mol Bol, Galveston, TX 77555 USA