title: Nucleomorphin. A novel, acidic, nuclear calmodulin-binding protein from dictyostelium that regulates nuclear number.
abstract: Probing of Dictyostelium discoideum cell extracts after SDS-PAGE using (35)S-recombinant calmodulin (CaM) as a probe has revealed approximately three-dozen Ca(2+)-dependent calmodulin binding proteins. Here, we report the molecular cloning, expression, and subcellular localization of a gene encoding a novel calmodulin-binding protein (CaMBP); we have called nucleomorphin, from D. discoideum. A lambdaZAP cDNA expression library of cells from multicellular development was screened using a recombinant calmodulin probe ((35)S-VU1-CaM). The open reading frame of 1119 nucleotides encodes a polypeptide of 340 amino acids with a calculated molecular mass of 38.7 kDa and is constitutively expressed throughout the Dictyostelium life cycle. Nucleomorphin contains a highly acidic glutamic/aspartic acid inverted repeat (DEED) with significant similarity to the conserved nucleoplasmin domain and a putative transmembrane domain in the carboxyl-terminal region. Southern blotting reveals that nucleomorphin exists as a single copy gene. Using gel overlay assays and CaM-agarose we show that bacterially expressed nucleomorphin binds to bovine CaM in a Ca(2+)-dependent manner. Amino-terminal fusion to the green fluorescence protein (GFP) showed that GFP-NumA localized to the nucleus as distinct arc-like patterns similar to heterochromatin regions. GFP-NumA lacking the acidic DEED repeat still showed arc-like accumulations at the nuclear periphery, but the number of nuclei in these cells was increased markedly compared with control cells. Cells expressing GFP-NumA lacking the transmembrane domain localized to the nuclear periphery but did not affect nuclear number or gross morphology. Nucleomorphin is the first nuclear CaMBP to be identified in Dictyostelium. Furthermore, these data present the first identification of a member of the nucleoplasmin family as a calmodulin-binding protein and suggest nucleomorphin has a role in nuclear structure in Dictyostelium.
authors.affiliation: Department of Zoology, University of Toronto at Mississauga, Mississauga, Ontario L5L 1C6, Canada.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Myre
authors.forename: Danton H
authors.initials: DH
authors.lastname: O'Day
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D002147:Calmodulin / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004023:Dictyostelium / Q000378:metabolism*; D015723:Gene Library; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D006570:Heterochromatin / Q000737:chemistry; D008164:Luminescent Proteins / Q000737:chemistry / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016366:Open Reading Frames; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014162:Transfection
chemical_list: D002147:Calmodulin; D002352:Carrier Proteins; D018076:DNA, Complementary; D006570:Heterochromatin; D008164:Luminescent Proteins; D009687:Nuclear Proteins; D015800:Protozoan Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins