1. T. M. Nakamura, J. Lingner, T. R. Cech, Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309–0215, USA.
2. G. B. Morin, K. B. Chapman, S. L. Weinrich, W. H. Andrews, C. B. Harley, Geron Corporation, 230 Constitution Drive, Menlo Park, CA 94025, USA.