, Volume 117, Issue 2, pp 149–158

SU(VAR)3-9 is a Conserved Key Function in Heterochromatic Gene Silencing


  • Gunnar Schotta
    • Institut für Genetik, BiologicumMartin-Luther-Universität Halle-Wittenberg
  • Anja Ebert
    • Institut für Genetik, BiologicumMartin-Luther-Universität Halle-Wittenberg
  • Gunter Reuter
    • Institut für Genetik, BiologicumMartin-Luther-Universität Halle-Wittenberg

DOI: 10.1023/A:1022923508198

Cite this article as:
Schotta, G., Ebert, A. & Reuter, G. Genetica (2003) 117: 149. doi:10.1023/A:1022923508198


This review summarizes genetic, molecular and biochemical studies of the SU(VAR)3-9 protein and the evidence for its key role in heterochromatin formation and heterochromatic gene silencing. The Su(var)3-9 locus was first identified as a dominant modifier of position-effect variegation (PEV) in Drosophila melanogaster. Together with Su(var)2-5 and Su(var)3-7, Su(var)3-9 belongs to the group of haplo-suppressor loci which show a triplo-dependent enhancer effect. All three genes encode heterochromatin-associated proteins. Su(var)3-9 is epistatic to the PEV modifier effects of Su(var)2-5 and Su(var)3-7, and it also dominates the effect of the Y chromosome on PEV. These genetic data support a central role of the SU(VAR)3-9 protein in heterochromatic gene silencing, one that is correlated with its activity as a histone H3-K9 methyltransferase (HMTase). In fact, SU(VAR)3-9 is the main chromocenter-specific HMTase of Drosophila. SU(VAR)3-9 and HP1, the product of Su(var)2-5, are main constituents of heterochromatin protein complexes and the interaction between these two proteins is interdependent. Functional analysis in fission yeast, Drosophila and mammals demonstrate that SU(VAR)3-9-dependent gene silencing processes are conserved in these organisms. This is also demonstrated by the rescue of Drosophila Su(var)3-9 mutant phenotypes with human SUV39H1 transgenes.

gene silencingheterochromatinSu(var)3-9
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© Kluwer Academic Publishers 2003