The HhH2/NDD domain of the Drosophila Nod chromokinesin-like protein is required for binding to chromosomes in the oocyte nucleus.
Nod is a chromokinesin-like protein that plays a critical role in segregating achiasmate chromosomes during female meiosis. The C-terminal half of the Nod protein contains two putative DNA-binding domains. The first of these domains, known as the HMGN domain, consists of three tandemly repeated high-mobility group N motifs. This domain was previously shown to be both necessary and sufficient for binding of the C-terminal half of Nod to mitotic chromosomes in embryos. The second putative DNA-binding domain, denoted HhH(2)/NDD, is a helix-hairpin-helix(2)/Nod-like DNA-binding domain. Although the HhH(2)/NDD domain is not required or sufficient for chromosome binding in embryos, several well-characterized nod mutations have been mapped in this domain. To characterize the role of the HhH(2)/NDD domain in mediating Nod function, we created a series of UAS-driven transgene constructs capable of expressing either a wild-type Nod-GFP fusion protein or proteins in which the HhH(2)/NDD domain had been altered by site-directed mutagenesis. Although wild-type Nod-GFP localizes to the oocyte chromosomes and rescues the segregation defect in nod mutant oocytes, two of three proteins carrying mutants in the HhH(2)/NDD domain fail to either rescue the nod mutant phenotype or bind to oocyte chromosomes. However, these mutant proteins do bind to the polytene chromosomes in nurse-cell nuclei and enter the oocyte nucleus. Thus, even though the HhH(2)/NDD domain is not essential for chromosome binding in other cell types, it is required for chromosome binding in the oocyte. These HhH(2)/NDD mutants also block the localization of Nod to the posterior pole of stage 9-10A oocytes, a process that is thought to facilitate the interaction of Nod with the plus ends of microtubules (Cui et al. 2005). This observation suggests that the Nod HhH2/NDD domain may play other roles in addition to binding Nod to meiotic chromosomes.
Cui
Wei
W
Stowers Institute for Medical Research, 1000 E. 50th Street, Kansas City, MO 64110, USA.
Hawley
R Scott
RS
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002875:Chromosomes / Q000378:metabolism*; D004330:Drosophila / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D049452:Green Fluorescent Proteins / Q000378:metabolism; D024001:HMGN Proteins / Q000235:genetics / Q000378:metabolism; D016547:Kinesins; D008540:Meiosis / Q000235:genetics / Q000502:physiology*; D008856:Microscopy, Fluorescence; D008868:Microtubule Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D017422:Sequence Analysis, DNA; D019076:Transgenes
D029721:Drosophila Proteins; D024001:HMGN Proteins; D008868:Microtubule Proteins; D049452:Green Fluorescent Proteins; C080298:Nod protein, Drosophila; D016547:Kinesins