Nucleomorphin

Abstract

Probing of Dictyostelium discoideum cell extracts after SDS-PAGE using 35 . 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.

Deficiency of Huntingtin Has Pleiotropic Effects in the Social Amoeba Dictyostelium discoideum

“…The resulting vector therefore expresses the first 14 amino acids of hd fused upstream of GFP, under the control of the predicted minimal hd promoter sequence. The vector was transformed into AX3 cells as previously described [71].…”

Rad53 homologue forkhead-associated kinase A (FhkA) and Ca2+-binding protein 4a (CBP4a) are nucleolar proteins that differentially redistribute during mitosis in Dictyostelium

“…NumA1 localizes predominately to nucleoli but is also present in the nucleoplasm [24,27]. NumA1 likely interacts with binding-partner puromycin-sensitive aminopeptidase A (PsaA) in the nucleoplasm, since this is where the two colocalize, however its nucleolar binding partner has yet to be identified [34,35].…”

“…CBP4a is one of 13 Ca 2+ -binding proteins (CBPs) in Dictyostelium and although its function remains unknown its interaction with NumA1 suggests that it may be involved in cell cycle events [36-40]. This is based on several lines of evidence linking NumA1 to the cell cycle such as its interaction with PsaA, a protein involved in cell cycle events, and the presence of several protein domains which are found in cell cycle proteins [27,34,41-43]. Recent studies on Dictyostelium PsaA localization and binding-proteins support its putative role in the cell cycle [42,43].…”

Proteins of the Nucleolus of Dictyostelium discoideum: Nucleolar Compartmentalization, Targeting Sequences, Protein Translocations and Binding Partners

“…Nucleomorphin isoform NumA1 represents the only verified nucleolar calmodulin-binding protein in Dictyostelium . Acting as a regulator of nuclear number and interacting with calmodulin in a Ca 2+ -dependent manner, it is predominantly a nucleolar protein with secondary nucleoplasmic localization [51,52,53]. This pattern of localization is a common feature of nucleolar proteins (e.g., nucleophosmin, adenosine deaminases, and murine double minute 2) that shuttle between the nucleolus and nucleoplasm [54,55].…”

“…Full length nucleomorphin contains a breast cancer carboxy-terminus domain (BRCT) that is found in cell cycle checkpoint proteins in other organisms [51,56]. The presence of a highly acidic, glu/asp domain is a common feature of nucleolar proteins including nucleophosmin, nucleoplasmin, nucleolin, and Hsp32 [26,28].…”