Topology of yeast Ndc1p: predictions for the human NDC1/NET3 homologue.
The nuclear pore complex is the predominant structure in the nuclear envelope that spans the double nuclear membranes of all eukaryotes. Yeasts have one additional organelle that is also embedded in the nuclear envelope: the spindle pole body, which functions as the microtubule organizing center. The only protein known to localize to and be important in the assembly of both of these yeast structures is the integral membrane protein, Ndc1p. However, no homologues of Ndc1p had been characterized in metazoa. Here, we identify and analyze NDC1 homologues that are conserved throughout evolution. We show that the overall topology of these homologues is conserved. Each contains six transmembrane segments in its N-terminal half and has a large soluble C-terminal half of approximately 300 amino acids. Charge distribution analysis infers that the N- and C-termini are exposed to the cytoplasm. Limited proteolysis of yeast Ndc1p in cellular membranes confirms the orientation of its C-terminus. Although it is not known whether vertebrate NDC1 protein localizes to nuclear pores like its yeast counterpart, the human homologue contains three FG repeats in the C-terminus, a feature of many nuclear pore proteins. Moreover, a small region containing mutations that affect assembly of the nuclear pore in yeast is highly conserved throughout evolution. Lastly, we bring together data from another study to demonstrate that the human homologue of NDC1 is the known inner nuclear membrane protein, NET3.
Lau
Corine K
CK
Section of Cell and Developmental Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, 92093, USA.
Delmar
Valerie A
VA
Forbes
Douglass J
DJ
D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D006801:Humans; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000737:chemistry / Q000235:genetics; D022022:Nuclear Pore / Q000737:chemistry / Q000235:genetics; D028861:Nuclear Pore Complex Proteins / Q000737:chemistry* / Q000235:genetics; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics; D010802:Phylogeny; D011237:Predictive Value of Tests; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
C082594:NDC1 protein, S cerevisiae; C510249:NDC1 protein, human; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins