Molecular characterization of homologues of both subunits A (SPO11) and B of the archaebacterial topoisomerase 6 in plants

The Spo11 protein is an eukaryotic homologue of the topoisomerase 6 subunit A from archaebacteria. In yeast Spo11p has been found to bind covalently t o double-strand breaks (DSBs) during meiosis. Single homologues of the SPO1 1 gene exist in various eukaryotes, except plants. Previously, we found in the Arabidopsis thaliana genome two ancient paralogs, AtSPO11-1 and 2. Here we report on the molecular characterization of a third one, AtSPO11-3. Thi s puzzling finding might be explained by the fact that we detected addition ally - for the first time outside of the archaebacterial kingdom - a homolo gue of the subunit B of topoisomerase 6, AtTOP6B. Both AtSPO11-3 and AtTOP6 B are abundantly expressed in Arabidopsis and EST comparisons indicate the presence of both genes in various plant species. Via two hybrid studies we could demonstrate that full length AtTop6B is able to interact with AtSpo11 -2 and 3 but not with AtSpo11-1. Our data suggest that plants possess in co ntrast to other eukaryotes an additional archaebacterial kind of topoisomer ase. (C) 2001 Elsevier Science B.V. All rights reserved.