title: Iron-inducible nuclear translocation of a Myb3 transcription factor in the protozoan parasite Trichomonas vaginalis.
abstract: In Trichomonas vaginalis, a novel nuclear localization signal spanning the folded R2R3 DNA-binding domain of a Myb2 protein was previously identified. To study whether a similar signal is used for nuclear translocation by other Myb proteins, nuclear translocation of Myb3 was examined in this report. When overexpressed, hemagglutinin-tagged Myb3 was localized to nuclei of transfected cells, with a cellular distribution similar to that of endogenous Myb3. Fusion to a bacterial tetracycline repressor, R2R3, of Myb3 that spans amino acids (aa) 48 to 156 was insufficient for nuclear translocation of the fusion protein, unless its C terminus was extended to aa 167. The conserved isoleucine in helix 2 of R2R3, which is important for Myb2's structural integrity in maintaining DNA-binding activity and nuclear translocation, was also vital for the former activity of Myb3, but less crucial for the latter. Sequential nuclear influx and efflux of Myb3, which require further extension of the nuclear localization signal to aa 180, were immediately induced after iron repletion. Sequence elements that regulate nuclear translocation with cytoplasmic retention, nuclear influx, and nuclear efflux were identified within the C-terminal tail. These results suggest that the R2R3 DNA-binding domain also serves as a common module for the nuclear translocation of both Myb2 and Myb3, but there are intrinsic differences between the two nuclear localization signals.
authors.affiliation: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Hong-Ming
authors.initials: HM
authors.lastname: Hsu
authors.forename: Yu
authors.initials: Y
authors.lastname: Lee
authors.forename: Dharmu
authors.initials: D
authors.lastname: Indra
authors.forename: Shu-Yi
authors.initials: SY
authors.lastname: Wei
authors.forename: Hsing-Wei
authors.initials: HW
authors.lastname: Liu
authors.forename: Lung-Chun
authors.initials: LC
authors.lastname: Chang
authors.forename: Chinpan
authors.initials: C
authors.lastname: Chen
authors.forename: Shiou-Jeng
authors.initials: SJ
authors.lastname: Ong
authors.forename: Jung-Hsiang
authors.initials: JH
authors.lastname: Tai
mesh_terms: D021581:Active Transport, Cell Nucleus; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D019913:Nuclear Localization Signals; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014246:Trichomonas vaginalis / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D019913:Nuclear Localization Signals; D015800:Protozoan Proteins; D014157:Transcription Factors; D007501:Iron