title: Identification of a single nuclear localization signal in the C-terminal domain of an Aspergillus DNA topoisomerase II.
abstract: DNA topoisomerase II (topo II) is a major nuclear protein that plays an important role in DNA metabolism. We have isolated the gene for topo II ( TOP2) from the filamentous fungus Aspergillus terreus. The deduced amino acid sequence revealed that topo II consists of 1,587 amino acids and has a calculated molecular weight of 180 kDa; the protein expressed in Escherichia coli has an estimated molecular weight of 185 kDa. Expression of topo II polypeptides tagged with yellow fluorescent protein (YFP) in budding yeast suggests that the C-terminal region of the topo II is essential for transport of the fusion protein into the nucleus. The nuclear localization signal (NLS) sequence of topo II is a non-classical bipartite type containing two interdependent, positively charged clusters separated by 15 amino acids. Alanine scanning mutagenesis and deletion analyses showed further that a stretch of 23 amino acid residues (positions 1,234-1,256) is necessary for nuclear import. In addition, we confirmed, using co-immunoprecipitation and two-hybrid analysis, that this non-classical NLS interacts with importin alpha in budding yeast. These results suggest that the fungal topo II NLS is functional in yeast cells.
authors.affiliation: Laboratory of Medical Mycology, Research Institute of Disease Mechanisms and Control, Nagoya University School of Medicine, 65 Tsurumai, Showa-ku, Nagoya, Aichi, 466-8550 Japan.
authors.forename: K-H
authors.initials: KH
authors.lastname: Kim
authors.forename: T
authors.initials: T
authors.lastname: Kanbe
authors.forename: T
authors.initials: T
authors.lastname: Akashi
authors.forename: I
authors.initials: I
authors.lastname: Mizuguchi
authors.forename: A
authors.initials: A
authors.lastname: Kikuchi
mesh_terms: D000595:Amino Acid Sequence; D001230:Aspergillus / Q000201:enzymology*; D001483:Base Sequence; D003001:Cloning, Molecular; D004250:DNA Topoisomerases, Type II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018076:DNA, Complementary; D004926:Escherichia coli / Q000235:genetics; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D011233:Precipitin Tests; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D018076:DNA, Complementary; D019913:Nuclear Localization Signals; D011994:Recombinant Proteins; D004250:DNA Topoisomerases, Type II