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D R Kellogg

Publications and source records attributed to D R Kellogg.

18 recordsLinked to original sources
PubMed2001

The Sda1 protein is required for passage through start.

We have used affinity chromatography to identify proteins that interact with Nap1, a protein previously shown to play a role in mitosis. Our studies demonstrate that a highly conserved protein called Sda1 binds to Nap1 both in vitro and in vivo. Loss of Sda1 function causes cells to arrest uniformly as unbudded cells that do not increase significantly in size. Cells arrested by loss of Sda1 function have a 1N DNA content, fail to produce the G1 cyclin Cln2, and remain responsive to mating pheromone, indicating that they arrest in G1 before Start. Expression of CLN2 from a heterologous promoter in temperature-sensitive sda1 cells induces bud emergence and polarization of the actin cytoskeleton, but does not induce cell division, indicating that the sda1 cell cycle arrest phenotype is not due simply to a failure to produce the G1 cyclins. The Sda1 protein is absent from cells arrested in G0 and is expressed before Start when cells reenter the cell cycle, further suggesting that Sda1 functions before Start. Taken together, these findings reveal that Sda1 plays a critical role in G1 events. In addition, these findings suggest that Nap1 is likely to function during G1. Consistent with this, we have found that Nap1 is required for viability in cells lacking the redundant G1 cyclins Cln1 and Cln2. In contrast to a previous study, we have found no evidence that Sda1 is required for the assembly or function of the actin cytoskeleton. Further characterization of Sda1 is likely to provide important clues to the poorly understood mechanisms that control passage through G1.

Cell Cycle↗
PubMed1995

Members of the NAP/SET family of proteins interact specifically with B-type cyclins.

Cyclin-dependent kinase complexes that contain the same catalytic subunit are able to induce different events at different times during the cell cycle, but the mechanisms by which they do so remain largely unknown. To address this problem, we have used affinity chromatography to identify proteins that bind specifically to mitotic cyclins, with the goal of finding proteins that interact with mitotic cyclins to carry out the events of mitosis. This approach has led to the identification of a 60-kD protein called NAP1 that interacts specifically with members of the cyclin B family. This interaction has been highly conserved during evolution: NAP1 in the Xenopus embryo interacts with cyclins B1 and B2, but not with cyclin A, and the S. cerevisiae homolog of NAP1 interacts with Clb2 but not with Clb3. Genetic experiments in budding yeast indicate that NAP1 plays an important role in the function of Clb2, while biochemical experiments demonstrate that purified NAP1 can be phosphorylated by cyclin B/p34cdc2 kinase complexes, but not by cyclin A/p34cdc2 kinase complexes. These results suggest that NAP1 is a protein involved in the specific functions of cyclin B/p34cdc2 kinase complexes. In addition to NAP1, we found a 43-kD protein in Xenopus that is homologous to NAP1 and also interacts specifically with B-type cyclins. This protein is the Xenopus homolog of the human SET protein, which was previously identified as part of a putative oncogenic fusion protein (Von Lindern et al., 1992).

Amino Acid Sequence↗
PubMed1995

NAP1 acts with Clb1 to perform mitotic functions and to suppress polar bud growth in budding yeast.

NAP1 is a 60-kD protein that interacts specifically with mitotic cyclins in budding yeast and frogs. We have examined the ability of the yeast mitotic cyclin Clb2 to function in cells that lack NAP1. Our results demonstrate that Clb2 is unable to carry out its full range of functions without NAP1, even though Clb2/p34CDC28-associated kinase activity rises to normal levels. In the absence of NAP1, Clb2 is unable to efficiently induce mitotic events, and cells undergo a prolonged delay at the short spindle stage with normal levels of Clb2/p34CDC28 kinase activity. NAP1 is also required for the ability of Clb2 to induce the switch from polar to isotropic bud growth. As a result, polar bud growth continues during mitosis, giving rise to highly elongated cells. Our experiments also suggest that NAP1 is required for the ability of the Clb2/p34CDC28 kinase complex to amplify its own production, and that NAP1 plays a role in regulation of microtubule dynamics during mitosis. Together, these results demonstrate that NAP1 is required for the normal function of the activated Clb2/p34CDC28 kinase complex, and provide a step towards understanding how cyclin-dependent kinase complexes induce specific events during the cell cycle.

Blotting, Northern↗
PubMed1995

CP60: a microtubule-associated protein that is localized to the centrosome in a cell cycle-specific manner.

DMAP190 is a microtubule-associated protein from Drosophila that is localized to the centrosome. In a previous study, we used affinity chromatography to identify proteins that interact with DMAP190, and identified a 60-kDa protein that we named DMAP60 (Kellogg and Alberts, 1992). Like DMAP190, DMAP60 interacts with microtubules and is localized to the centrosome, and the two proteins associate as part of a multiprotein complex. We now report the cloning and sequencing of the cDNA encoding DMAP60. The amino acid sequence of DMAP60 is not homologous to any protein in the database, although it contains six consensus sites for phosphorylation by cyclin-dependent kinases. As judged by in situ hybridization, the gene for DMAP60 maps to chromosomal region 46A. In agreement with others working on Drosophila centrosomal proteins, we have changed the names for DMAP190 and DMAP60 to CP190 and CP60, respectively, to give these proteins a consistent nomenclature. Antibodies that recognize CP60 reveal that it is localized to the centrosome in a cell cycle-dependent manner. The amount of CP60 at the centrosome is maximal during anaphase and telophase, and then drops dramatically during late telophase or early interphase. This dramatic disappearance of CP60 may be due to specific proteolysis, because CP60 contains a sequence of amino acids similar to the "destruction box" that targets cyclins for proteolysis at the end of mitosis. Starting with nuclear cycle 12, CP60 and CP190 are both found in the nucleus during interphase. CP60 isolated from Drosophila embryos is highly phosphorylated, and dephosphorylated CP60 is a good substrate for cyclin B/p34cdc2 kinase complexes. A second kinase activity capable of phosphorylating CP60 is present in the CP60/CP190 multiprotein complex. We find that bacterially expressed CP60 binds to purified microtubules, and this binding is blocked by CP60 phosphorylation.

Amino Acid Sequence↗
PubMed1994

Isolation of cytoskeletal proteins from Drosophila.

In this summary of methods, we have attempted to present a series of protocols relevant to the study of proteins that associate with each other inside cells. These techniques have found their main application, in our hands, to cytoskeletal structures, but the utility of these techniques is limited to this application. As we learn more about the physiology and organization of eukaryotic cells, information from a variety of studies and systems indicates that many processes occur in a highly spatially organized manner in cells, using multiprotein complexes. The techniques described here will find application to the study of how organization and associations between proteins contribute to many of cellular processes.

Animals↗
PubMed1993

Drosophila gamma-tubulin is part of a complex containing two previously identified centrosomal MAPs.

gamma-tubulin is a minor tubulin that is localized to the microtubule organizing center of many fungi and higher eucaryotic cells (Oakley, B. R., C. E. Oakley, Y. Yoon, and M. C. Jung. 1990. Cell. 61: 1289-1301; Stearns, T., L. Evans, and M. Kirschner. 1991. Cell. 65:825-836; Zheng, Y., M. K. Jung, and B. R. Oakley. 1991. Cell. 65:817-823). Here we show that gamma-tubulin is a component of a previously isolated complex of Drosophila proteins that contains at least two centrosomal microtubule-associated proteins called DMAP190 and DMAP60. Like DMAP190 and DMAP60, the gamma-tubulin in extracts of early Drosophila embryos binds to microtubules, although this binding may be indirect. Unlike DMAP190 and DMAP60, however, only 10-50% of the gamma-tubulin in the extract is able to bind to microtubules. We show that gamma-tubulin binds to a microtubule column as part of a complex, and a substantial fraction of this gamma-tubulin is tightly associated with DMAP60. As neither alpha- nor beta-tubulin bind to microtubule columns, the gamma-tubulin cannot be binding to such columns in the form of an alpha:gamma or beta:gamma heterodimer. These observations suggest that gamma-tubulin, DMAP60, and DMAP190 are components of a centrosomal complex that can interact with microtubules.

Animals↗
PubMed1992

Purification of a multiprotein complex containing centrosomal proteins from the Drosophila embryo by chromatography with low-affinity polyclonal antibodies.

A 190-kDa centrosomal protein interacts with microtubules when Drosophila embryo extracts are passed over microtubule-affinity columns. We have obtained a partial cDNA clone that encodes this protein. Using a fusion protein produced from the clone, we have developed a novel immunoaffinity chromatography procedure that allows both the 190-kDa protein and a complex of proteins that associates with it to be isolated in in a single step. For this procedure, the fusion protein is used as an antigen to prepare rabbit polyclonal antibodies, and those antibodies that recognize the 190-kDa protein with low affinity are selectively purified on a column containing immobilized antigen. These low-affinity antibodies are then used to construct an immunoaffinity column. When Drosophila embryo extracts are passed over this column, the 190-kDa protein is quantitatively retained and can be eluted in nearly pure form under nondenaturing conditions with 1.5 M MgCl2, pH 7.6. The immunoaffinity column is washed with 1.0 M KCl just before the elution with 1.5 M MgCl2. This wash elutes 10 major proteins, as well as a number of minor ones. We present evidence that these KCl-eluted proteins represent additional centrosomal components that interact with the 190-kDa protein to form a multiprotein complex within the cell.

Animals↗
PubMed1989

Identification of microtubule-associated proteins in the centrosome, spindle, and kinetochore of the early Drosophila embryo.

We have developed affinity chromatography methods for the isolation of microtubule-associated proteins (MAPs) from soluble cytoplasmic extracts and have used them to analyze the cytoskeleton of the early Drosophila embryo. More than 50 Drosophila embryo proteins bind to microtubule affinity columns. To begin to characterize these proteins, we have generated individual mouse polyclonal antibodies that specifically recognize 24 of them. As judged by immunofluorescence, some of the antigens localize to the mitotic spindle in the early Drosophila embryo, while others are present in centrosomes, kinetochores, subsets of microtubules, or a combination of these structures. Since 20 of the 24 antibodies stain microtubule structures, it is likely that most of the proteins that bind to our columns are associated with microtubules in vivo. Very few MAPS seem to be identically localized in the cell, indicating that the microtubule cytoskeleton is remarkably complex.

Alkaloids↗
PubMed1988

Behaviour of microtubules and actin filaments in living Drosophila embryos.

We describe the preparation of novel fluorescent derivatives of rabbit muscle actin and bovine tubulin, and the use of these derivatives to study the behaviour of actin filaments and microtubules in living Drosophila embryos, in which the nuclei divide at intervals of 8 to 21 min. The fluorescently labelled proteins appear to function normally in vitro and in vivo, and they allow continuous observation of the cytoskeleton in living embryos without perturbing development. By coinjecting labelled actin and tubulin into the early syncytial embryo, the spatial relationships between the distinct filament networks that they form can be followed second by second. The dynamic rearrangements of actin filaments and microtubules observed confirms and extends results obtained from previous studies, in which fixation techniques and specific staining were used to visualize the cytoskeleton in the Drosophila embryo. However, no tested fixation method produces an exact representation of the in vivo microtubule distribution.

Actins↗
PubMed1971

Purpura fulminans.

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Amputation, Surgical↗