A balance between two nuclear localization sequences and a nuclear export sequence governs extradenticle subcellular localization.
During animal development, transcription factor activities are modulated by several means, including subcellular localization. The Hox cofactor Extradenticle (Exd) has a dynamic subcellular localization, such that Exd is cytoplasmic by default, but is nuclear when complexed with another homeodomain protein, Homothorax (Hth). These observations raise the question of whether dimerization with Hth simply induces Exd's nuclear localization or, alternatively, if Hth is also necessary for Exd activity. To address this question, we analyzed the nuclear transport signals in Exd, including a divergent nuclear export signal (NES) and two nuclear localization signals (NLSs). We show that, although these signals are weak compared to canonical signals, they balance each other in Exd. We also provide evidence that Exd contains an NLS mask that contributes to its cytoplasmic localization. With these signals characterized, we generated forms of Exd that are nuclear localized in the absence of Hth. Surprisingly, although these Exd forms are functional, they do not phenocopy Hth overexpression. These findings suggest that Hth is required for Exd activity, not simply for inducing its nuclear localization.
Stevens
Katherine E
KE
Department of Genetics and Development, Columbia University, New York, New York 10032, USA.
Mann
Richard S
RS
D021581:Active Transport, Cell Nucleus / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D049790:Nuclear Export Signals / Q000235:genetics*; D019913:Nuclear Localization Signals / Q000235:genetics* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013347:Subcellular Fractions / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic
D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D014157:Transcription Factors; C083405:exd protein, Drosophila; C108704:hth protein, Drosophila