[1] So Methodist Univ, Dept Biol Sci, Mol Virol Lab, Dallas, TX 75275 USA
[2] Free Univ Brussels, Inst Biol & Med Mol, Chim Biol Lab, B-6041 Gosselies, Belgium
[3] NCI, Lab Receptor Biol & Gene Express, Fluorescence Imaging Facil, Ctr Canc Res ,NIH, Bethesda, MD 20892 USA