Division of Biology, University of California at San Diego, La Jolla, CA 920930116, , USA1
Institute of Molecular Biology, National Chung Hsing University, Taichung, 402, Taiwan, , Republic of China2
Author for correspondence: M. H. Saier, Jr. Tel: + 1 858 534 4084. Fax: + 1 858 534 7108. e-mail: msaier{at}ucsd.edu