Identification of nuclear localization signals of Drosophila G9a histone H3 methyltransferase

G9a is one of the well-characterized histone methyltransferases. G9a regulates H3K9 mono- and dimethylation at euchromatic region and consequently plays important roles in euchromatic gene regulation. Mammalian G9a contains several distinct domains, such as GHD (G9a homology domain), ANK, preSET, SET and PostSET. These domains are highly conserved between mammals and Drosophila. Although mammalian G9a has nuclear localization signal (NLS) in its N-terminal region, the amino acid sequences of this region are not conserved in Drosophila. Here we have examined the subcellular localization of a series of truncated forms of Drosophila G9a (dG9a). The identified region (aa337-aa470) responsible for nuclear localization of dG9a contains four short stretches of positively charged basic amino acids (NLS1, aa334-aa345; NLS2, aa366-aa378; NLS3, aa407-aa419; NLS4, aa461-aa472). Each of NLS1, NLS3 and NLS4 is sufficient for the nuclear localization when they are fused with the enhanced green fluorescent protein. These NLSs of dG9a are distinct from those of mammalian G9a in their positions and amino acid sequences.