1. A. Shilatifard, R. C. Conaway, J. W. Conaway, Program in Molecular and Cell Biology, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA.
2. W. S. Lane, Harvard Microchemistry Facility, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
3. K. W. Jackson, William K. Warren Medical Research Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73190, USA.