Su(z)12, a novel Drosophila Polycomb group gene that is conserved in vertebrates and plants

In both Drosophila and vertebrates, spatially restricted expression of HOX genes is controlled by the Polycomb group (PcG) repressors. Here we charact erize a novel Drosophila PcG gene, Suppressor of zeste 12 (Su(z)12). Su(z)1 2 mutants exhibit very strong homeotic transformations and Su(z)12 function is required throughout development to maintain the repressed state of HOX genes. Unlike most other PcG mutations, Su(z)12 mutations are strong suppre ssors of position-effect variegation (PEV), suggesting that Su(z)12 also fu nctions in heterochromatin-mediated repression. Furthermore, Su(z)12 functi on is required for germ cell development. The Su(z)12 protein is highly con served in vertebrates and is related to the Arabidopsis proteins EMF2, FIS2 and VRN2. Notably, EMF2 is a repressor of floral homeotic genes. These res ults suggest that at least some of the regulatory machinery that controls h omeotic gene expression is conserved between animals and plants.