1. Department of Molecular Genetics and Microbiology; University of New Mexico School of Medicine; Albuquerque; New Mexico 87131; USA
2. Department of Immunobiology, The BIO5 Institute; University of Arizona; Tucson; AZ; 85721; USA
3. International Centre for Genetic Engineering and Biotechnology; Padriciano 99; I-34149 Trieste; Italy