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Distinct biochemical requirements for the budding, targeting and fusion òf ER-derived transport vesicles
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Interaction of bride of sevenless membrane-bound Iigand and the sevenless tyrosine-kinase receptor H. Kr~mer, R. L. Cagan and S. L. Zipursky Nature 352, 207-212 In the developing compound eye of Drosophila, each ommatidium develops around a cluster of eight photoreceptor cells (R1-8). For development of the R7 cell, the sevenless (sev) gene, which encodes a transmembrane tyrosine kinase receptor, is required in the R7 cell itself, whereas the bride of sevenless (boss) gene is required in the neighbouring R8 cell; the boss protein is thus thought to be the inductive ligand for the receptor sev. Surprisingly for the gene of a putative ligand,
boss encodes a transmembrane protein, with seven predicted membrane-spanning regions and a large extracellular domain. The evidence presented in this paper indicates boss is indeed the ligand for sev. In suspensions of cells that expressed boss and sev, only heterotypic aggregates formed. Immunolocalization studies showed that boss was located at the apical surface of R8 cells in the developing ommatidial cluster; interestingly, sev has been previously localized to the
Distinct biochemical requirements for the budding, targeting and fusion ~f ER-derived transport vesicles M. F. Rexach and R. W. Schekman J. Cell Biol. 114, 219-229 The secretory pathway in Saccharomyces cerevisiae was broadly defined more than a decade ago by the isolation of mutants defective in each step. The studies were extended by electron microscopy of mutant strains, which revealed that some mutations cause the accumulation of
vesicles that appear to be Intermediates in the secretory pathway. In this paper, the authors demonstrate the presence of a vesicular intermediate in a cell-free assay that reconstitutes ER-Golgi transport in broken cell preparations from yeast. The formation of putative transport vesicles
Characterization of an immediate-early gene induced In adherent monocytes that encodes i~B-Iike activity S. Haskill et al. Cell 65, 1281-1289 "See the next issue of TCB for a review of nuclear-uptake regulatory proteins,
84
The activity of the transcription factor NF-~cB is regulated by the protein I~B'. In unstimulated cells, I~B sequesters NF-lcB in the cytoplasm and inhibits its DNA-binding activity. Stimulation by various agents results in dissociation of the NF-KB-I~B complex, probably as a result of
phosphorylation of IKB, and the induction of nuclear NF-lcB DNAbinding activity. The I~:B activity has not yet been fully purified. Here, a gene whose expression is rapidly induced in human monocytes upon adherence (MAD-3) has been found to encode a protein with
apical surface of surrounding cells. In addition, boss was detected in large multivesicular bodies in R7 cells, and it was shown that the internalization of the protein into R7 cells was dependent on the presence of sev. The results pose many new questions for both cell and developmental biology: for example, how does a membrane-bound iigand enter another cell, and how is internalization of boss apparently restricted to the prospective R7 cell?
required the S£C12 and SEC23 gene products. Mutations in these genes lead to defects in vesicle formation in vivo. Transport vesicle formation also required ATP and GTP hydrolysis. Targeting of the vesicles to the Golgi required the YPT1 gene product, a GTP-binding protein already known to be involved in secretion, and the SEC18 gene product, a putative vesicle.fusion protein. Fusion of the vesicles with the acceptor required Ca2+ and ATP. Purification of these transport vesicles should allow the definition of their components and help us to understand how they are faithfully targeted to their correct acceptor compartment along the secretory pathway.
I~B.like characteristics; for example, the size of the protein is similar to that of I~B, and in vitro translated MAD-3 protein specifically inhibits DNA-binding activity of NF-~B. The predicted sequence of MAD-3 includes several putative protein kinase consensus target sequences and five tandem repeats of the SWl6/ankyrin motif, which is implicated in binding to cytoskeletal proteins and integral membrane proteins. Similar SWl6/ankyrin repeats are present in the precursor of the p50 subunit of NF-IcB, and the authors suggest that these regions may form the basis for a common subcellular localization.
TRENDS IN CELLBIOLOGYVOL. 1 OCTOBER1991
E
Interaction of bride of sevenless membrane-bound Iigand and the sevenless tyrosine-kinase receptor H. Kr~mer, R. L. Cagan and S. L. Zipursky Nature 352, 207-212 In the developing compound eye of Drosophila, each ommatidium develops around a cluster of eight photoreceptor cells (R1-8). For development of the R7 cell, the sevenless (sev) gene, which encodes a transmembrane tyrosine kinase receptor, is required in the R7 cell itself, whereas the bride of sevenless (boss) gene is required in the neighbouring R8 cell; the boss protein is thus thought to be the inductive ligand for the receptor sev. Surprisingly for the gene of a putative ligand,
boss encodes a transmembrane protein, with seven predicted membrane-spanning regions and a large extracellular domain. The evidence presented in this paper indicates boss is indeed the ligand for sev. In suspensions of cells that expressed boss and sev, only heterotypic aggregates formed. Immunolocalization studies showed that boss was located at the apical surface of R8 cells in the developing ommatidial cluster; interestingly, sev has been previously localized to the
Distinct biochemical requirements for the budding, targeting and fusion ~f ER-derived transport vesicles M. F. Rexach and R. W. Schekman J. Cell Biol. 114, 219-229 The secretory pathway in Saccharomyces cerevisiae was broadly defined more than a decade ago by the isolation of mutants defective in each step. The studies were extended by electron microscopy of mutant strains, which revealed that some mutations cause the accumulation of
vesicles that appear to be Intermediates in the secretory pathway. In this paper, the authors demonstrate the presence of a vesicular intermediate in a cell-free assay that reconstitutes ER-Golgi transport in broken cell preparations from yeast. The formation of putative transport vesicles
Characterization of an immediate-early gene induced In adherent monocytes that encodes i~B-Iike activity S. Haskill et al. Cell 65, 1281-1289 "See the next issue of TCB for a review of nuclear-uptake regulatory proteins,
84
The activity of the transcription factor NF-~cB is regulated by the protein I~B'. In unstimulated cells, I~B sequesters NF-lcB in the cytoplasm and inhibits its DNA-binding activity. Stimulation by various agents results in dissociation of the NF-KB-I~B complex, probably as a result of
phosphorylation of IKB, and the induction of nuclear NF-lcB DNAbinding activity. The I~:B activity has not yet been fully purified. Here, a gene whose expression is rapidly induced in human monocytes upon adherence (MAD-3) has been found to encode a protein with
apical surface of surrounding cells. In addition, boss was detected in large multivesicular bodies in R7 cells, and it was shown that the internalization of the protein into R7 cells was dependent on the presence of sev. The results pose many new questions for both cell and developmental biology: for example, how does a membrane-bound iigand enter another cell, and how is internalization of boss apparently restricted to the prospective R7 cell?
required the S£C12 and SEC23 gene products. Mutations in these genes lead to defects in vesicle formation in vivo. Transport vesicle formation also required ATP and GTP hydrolysis. Targeting of the vesicles to the Golgi required the YPT1 gene product, a GTP-binding protein already known to be involved in secretion, and the SEC18 gene product, a putative vesicle.fusion protein. Fusion of the vesicles with the acceptor required Ca2+ and ATP. Purification of these transport vesicles should allow the definition of their components and help us to understand how they are faithfully targeted to their correct acceptor compartment along the secretory pathway.
I~B.like characteristics; for example, the size of the protein is similar to that of I~B, and in vitro translated MAD-3 protein specifically inhibits DNA-binding activity of NF-~B. The predicted sequence of MAD-3 includes several putative protein kinase consensus target sequences and five tandem repeats of the SWl6/ankyrin motif, which is implicated in binding to cytoskeletal proteins and integral membrane proteins. Similar SWl6/ankyrin repeats are present in the precursor of the p50 subunit of NF-IcB, and the authors suggest that these regions may form the basis for a common subcellular localization.
TRENDS IN CELLBIOLOGYVOL. 1 OCTOBER1991