A schematic figure showing the architectures of proteins containing XS domains. More information about the ring finger domain, the CBS domain and the GADD45/L7/L30 domain can be found in the Pfam database  at http://www.sanger.ac.uk/Software/Pfam with accession numbers PF00097, PF00571 and PF01248 respectively. The asterisk denotes where the domain architecture shown is not from ring finger in rice gene X (Q9SBW2) sequence deposited in the protein database but is that found in the manuscript by Chen et al. . The XS, XH and the zinc finger found in SGS3 have been submitted to Pfam and given accession numbers PF03468, PF03469, PF03470 respectively.