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KAR5 encodes a novel pheromone-inducible protein required for homotypic nuclear fusion.

Beh CT, Brizzio V, Rose MD - J. Cell Biol. (1997)

Bottom Line: KAR5 encodes a novel protein that shares similarity with a protein in Schizosaccharomyces pombe that may play a similar role in nuclear fusion.Kar5p is a membrane protein with its soluble domain entirely contained within the lumen of the endoplasmic reticulum.In pheromone-treated cells, Kar5p was localized to the vicinity of the spindle pole body, the initial site of fusion between haploid nuclei during karyogamy.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544-1014, USA.

ABSTRACT
KAR5 is required for membrane fusion during karyogamy, the process of nuclear fusion during yeast mating. To investigate the molecular mechanism of nuclear fusion, we cloned and characterized the KAR5 gene and its product. KAR5 is a nonessential gene, and deletion mutations produce a bilateral defect in the homotypic fusion of yeast nuclei. KAR5 encodes a novel protein that shares similarity with a protein in Schizosaccharomyces pombe that may play a similar role in nuclear fusion. Kar5p is induced as part of the pheromone response pathway, suggesting that this protein uniquely plays a specific role during mating in nuclear membrane fusion. Kar5p is a membrane protein with its soluble domain entirely contained within the lumen of the endoplasmic reticulum. In pheromone-treated cells, Kar5p was localized to the vicinity of the spindle pole body, the initial site of fusion between haploid nuclei during karyogamy. We propose that Kar5p is required for the completion of nuclear membrane fusion and may play a role in the organization of the membrane fusion complex.

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The primary sequence of Kar5p predicts a transmembrane protein with a region of coiled-coil. Kar5p has three regions of significantly hydrophobic character. Shown are (A) Hopp-Woods hydrophilicity and (B) Kyte-Doolittle hydropathy plots.  The hydrophobic regions are shown as gray bars. Kar5p also has  two or more regions predicted to form a coiled-coil. (C) A plot of  the probability of forming a coiled-coil according to the algorithm  of Lupas (1996). (D) A comparison of the predicted structures  for S. cerevisiae Kar5p and the S. pombe Tht1p. See text for details.
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Figure 3: The primary sequence of Kar5p predicts a transmembrane protein with a region of coiled-coil. Kar5p has three regions of significantly hydrophobic character. Shown are (A) Hopp-Woods hydrophilicity and (B) Kyte-Doolittle hydropathy plots. The hydrophobic regions are shown as gray bars. Kar5p also has two or more regions predicted to form a coiled-coil. (C) A plot of the probability of forming a coiled-coil according to the algorithm of Lupas (1996). (D) A comparison of the predicted structures for S. cerevisiae Kar5p and the S. pombe Tht1p. See text for details.

Mentions: Three regions of the Kar5p protein were predicted to be significantly hydrophobic (Figs. 2 B and 3). The first corresponds to the amino-terminal 20 residues and may therefore correspond to a secretory signal sequence. However, since no sites were found that conform to the consensus -3,-1 rule for a signal peptide cleavage site (von Heijne, 1986), if the NH2-terminal sequence does function as is a signal peptide, it may not be cleaved. Two other regions predicted to form significantly hydrophobic regions were found towards the carboxyl terminus (residues 455–470 and 485–502), and these may form transmembrane spanning domains, although no strong predictions about the orientation can be made (Hofmann and Stoffel, 1993; Rost et al., 1995). Taken together, the primary structure suggests that Kar5p enters the secretory pathway and is an integral membrane protein with one or more carboxy-terminal regions spanning the membrane.


KAR5 encodes a novel pheromone-inducible protein required for homotypic nuclear fusion.

Beh CT, Brizzio V, Rose MD - J. Cell Biol. (1997)

The primary sequence of Kar5p predicts a transmembrane protein with a region of coiled-coil. Kar5p has three regions of significantly hydrophobic character. Shown are (A) Hopp-Woods hydrophilicity and (B) Kyte-Doolittle hydropathy plots.  The hydrophobic regions are shown as gray bars. Kar5p also has  two or more regions predicted to form a coiled-coil. (C) A plot of  the probability of forming a coiled-coil according to the algorithm  of Lupas (1996). (D) A comparison of the predicted structures  for S. cerevisiae Kar5p and the S. pombe Tht1p. See text for details.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2140214&req=5

Figure 3: The primary sequence of Kar5p predicts a transmembrane protein with a region of coiled-coil. Kar5p has three regions of significantly hydrophobic character. Shown are (A) Hopp-Woods hydrophilicity and (B) Kyte-Doolittle hydropathy plots. The hydrophobic regions are shown as gray bars. Kar5p also has two or more regions predicted to form a coiled-coil. (C) A plot of the probability of forming a coiled-coil according to the algorithm of Lupas (1996). (D) A comparison of the predicted structures for S. cerevisiae Kar5p and the S. pombe Tht1p. See text for details.
Mentions: Three regions of the Kar5p protein were predicted to be significantly hydrophobic (Figs. 2 B and 3). The first corresponds to the amino-terminal 20 residues and may therefore correspond to a secretory signal sequence. However, since no sites were found that conform to the consensus -3,-1 rule for a signal peptide cleavage site (von Heijne, 1986), if the NH2-terminal sequence does function as is a signal peptide, it may not be cleaved. Two other regions predicted to form significantly hydrophobic regions were found towards the carboxyl terminus (residues 455–470 and 485–502), and these may form transmembrane spanning domains, although no strong predictions about the orientation can be made (Hofmann and Stoffel, 1993; Rost et al., 1995). Taken together, the primary structure suggests that Kar5p enters the secretory pathway and is an integral membrane protein with one or more carboxy-terminal regions spanning the membrane.

Bottom Line: KAR5 encodes a novel protein that shares similarity with a protein in Schizosaccharomyces pombe that may play a similar role in nuclear fusion.Kar5p is a membrane protein with its soluble domain entirely contained within the lumen of the endoplasmic reticulum.In pheromone-treated cells, Kar5p was localized to the vicinity of the spindle pole body, the initial site of fusion between haploid nuclei during karyogamy.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544-1014, USA.

ABSTRACT
KAR5 is required for membrane fusion during karyogamy, the process of nuclear fusion during yeast mating. To investigate the molecular mechanism of nuclear fusion, we cloned and characterized the KAR5 gene and its product. KAR5 is a nonessential gene, and deletion mutations produce a bilateral defect in the homotypic fusion of yeast nuclei. KAR5 encodes a novel protein that shares similarity with a protein in Schizosaccharomyces pombe that may play a similar role in nuclear fusion. Kar5p is induced as part of the pheromone response pathway, suggesting that this protein uniquely plays a specific role during mating in nuclear membrane fusion. Kar5p is a membrane protein with its soluble domain entirely contained within the lumen of the endoplasmic reticulum. In pheromone-treated cells, Kar5p was localized to the vicinity of the spindle pole body, the initial site of fusion between haploid nuclei during karyogamy. We propose that Kar5p is required for the completion of nuclear membrane fusion and may play a role in the organization of the membrane fusion complex.

Show MeSH