Originally published as Genetics Published Articles Ahead of Print on September 2, 2005.

Genetics, Vol. 171, 1823-1835, December 2005, Copyright © 2005
doi:10.1534/genetics.105.047464

The HhH(2)/NDD Domain of the Drosophila Nod Chromokinesin-like Protein Is Required for Binding to Chromosomes in the Oocyte Nucleus

* Stowers Institute for Medical Research, Kansas City, Missouri 64110, {dagger} Department of Pathology and Clinical Laboratory, The University of Kansas Medical Center, Kansas City, Kansas 66160 and {ddagger} Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66045

1 Corresponding author: Stowers Institute for Medical Research, 1000 E. 50th St., Kansas City, MO 64110.
E-mail: rsh{at}stowers-institute.org

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.




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