1. Department of Biochemistry and Molecular Biology, Dalhousie University Halifax NS, Canada B3H 1X5; E-mail: andrew.roger@dal.ca (A.J.R.)
2. Department of Mathematics and Statistics and Genome Atlantic, Dalhousie University Halifax NS, Canada B3H 3J5
3. Department für Biologie I, Botanik, Ludwig-Maximilians-Universität München Menzingerstraße 67, D-80638 München, Germany