[1] Univ Barcelona, Fac Biol, Dept Genet, E-08071 Barcelona, Spain
[2] NCI, Intramural Res Support Program, SAIC Frederick, Frederick Canc Res & Dev Ctr, Frederick, MD 21702 USA
[3] Fdn Jimenez Diaz, Dept Genet, E-28040 Madrid, Spain
[4] NCI, Lab Gen Divers, Frederick Canc Res & Dev Ctr, Frederick, MD 21702 USA