Fingerprinting fission yeast: polymorphic markers for molecular genetic analysis of Schizosaccharomyces pombe strains.

The fission yeast Schizosaccharomyces pombe is widely used as a model eukaryote for cell and molecular studies but little is known of natural genetic variation in this species. In order to obtain informative molecular markers, imperfect tandem repeats, identified through bioinformatic methods, were tested for length polymorphism in six wild-type strains of Sch. pombe isolated from different substrates and geographical locations in Africa, America, Asia and Europe. Of 26 loci tested, 21 were multi-allelic, consistent with tandem repeat copy number variation. Eleven of these polymorphic tandem repeats are in regions encoding intracellular proteins. Most of the protein-coding repeats are not sited within structured domains but have non-regular predicted structure; one has a repeat unit length corresponding to integer turns of a predicted amphipathic alpha-helix secondary structure, suggesting that this repeat may be tolerated because copy number mutations change alpha-helix length but not orientation within the protein structure. In contrast to the differences observed between natural isolates of Sch. pombe, genetic strains were found to be essentially isogenic: only two polymorphic loci were detected out of 26 minisatellites and five microsatellites tested in 16 strains, including a hypervariable microsatellite in the med15 gene. The polymorphic tandem repeat markers identified in this study will prove useful for DNA fingerprinting and molecular analysis of natural genetic variation in Sch. pombe isolates.