[1] Inst Pasteur, Dept Biotechnol, CNRS, Unite Virus Oncogenes 1644, F-75724 Paris 15, France
[2] Inst Pasteur, Dept Biotechnol, Lab Hybridolab, F-75724 Paris, France
[3] Univ London Univ Coll, Eisai London Res Labs, London WC1E 6BT, England
[4] Texas Tech Univ, Sch Med, Dept Cell Biol & Biochem, Lubbock, TX USA