BMC Genomics 2008, 9:308 http://www.biomedcentral.com/1471-2164/9/308 RFeigpurerese4ntative full sequence alignment of the PRC1 Ring family Representative full sequence alignment of the PRC1 Ring family. The coloring scheme indicates average BLOSUM62 score (correlated to amino acid conservation) in each alignment column: red (greater than 4), violet (between 4 and 1.5) and light yellow (between 1.5 and 0.5). The sequences are named as described in Figure 1. Lowercase characters represent parts of the sequence that are not evolutionarily conserved. In the PRC1 Ring family the N-terminal Ring domain (blue rectangle) is more conserved than the C-terminal RAWUL domain (green rectangle). account the fact that convergent evolution of domain architectures is rare [76], the common domain architec- ture presented by the plants and animal PRC1 Ring finger proteins (Figure 3) suggest a common evolutionary ori- gin, raising the possibility that these plant proteins could be the PRC1 Ring finger orthologs, in turn implying that the PRC1-mediated histone H2A ubiquitination might also take place in plant. called Terminal Flower2, TFL2) is functionally similar to Pc, a subunit of PRC1 that recognizes and binds the H3K27 marks created by PRC2. Similarly, PRC1 Ring fin- ger proteins were thought to be missing in plants; how- ever, our analysis revealed the presence of putative orthologs to these proteins. All together these data suggest that PRC1 is also conserved in plants, in agreement with our analysis. Plants were thought to have no homologs of PRC1 com- ponents. However, two recent reports (25,26) shows that Arabidopsis Like Heterochromatin Protein1 (LHP1, also Based on sequence similarity and biochemical data, two groups of PRC1 Ring finger proteins have been defined [18,36], the Bmi1 subfamily that includes vertebrate Bmi1 Page 7 of 11 (page number not for citation purposes)