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Mutations in the Drosophila genes pimples and three rows result in a defect of sister chromatid separation during mitosis. As a consequence, cytokinesis is also defective. However, cell cycle progression including the mitotic degradation of cyclins A and B is not blocked by the failure of sister chromatid separation, and as a result, metaphase chromosomes with twice the normal number of chromosome...
We isolated a cDNA clone encoding a kinesin-related protein, which we named XKCM1. Antibodies to XKCM1 stain mitotic centromeres and spindle poles. Immunodepletion and antibody addition experiments in an in vitro spindle assembly assay show that XKCM1 is required for both establishment and maintenance of mitotic spindles. The structures that form in the absence of XKCM1 contain abnormally long microtubules...
Replication machines use ring-shaped clamps that encircle DNA to tether the polymerase to the chromosome. The clamp is assembled on DNA by a clamp loader. This report shows that the polymerase and clamp loader coordinate their actions with the clamp by competing for it through overlapping binding sites. The competition is modulated by DNA. In the absence of DNA, the clamp associates with the clamp...
The frequencies of certain periodic behaviors of the nematode C. elegans are regulated in a dose-dependent manner by the activity of the gene egl-10. These behaviors are modulated oppositely by the activity of the G protein α subunit gene goa-1, suggesting that egl-10 may regulate a G protein signaling pathway in a dose-dependent fashion. egl-10 encodes a protein similar to Sst2p, a negative regulator...
We provide evidence that FGF8 serves as an endogenous inducer of chick limb formation and that its expression in the intermediate mesoderm at the appropriate time and place to trigger forelimb development is directly linked to the mechanism of embryonic kidney differentiation. One function of the limb inducer is to initiate Fgf8 gene expression in the ectoderm overlying the prospective limb-forming...
Using fluorescence in situ hybridization to extracted metaphase chromosomes, we present visual evidence that specific human DNA sequences occupy distinctive positions with respect to the axial region of chromosomes and that the DNA is organized into loops emanating from this region. In a stretch of unique DNA on chromosome 11, large loops of DNA can be traced and one specific region associated with...
Dividing cells must coordinate cell cycle events to ensure genetic stability. Here we identify an essential two-component signal transduction protein that controls multiple events in the Caulobacter cell cycle, including cell division, stalk synthesis, and cell cycle–specific transcription. This protein, CtrA, is homologous to response regulator transcription factors and controls transcription from...
We have determined the 2.0 Å crystal structure of a fragment of human fibronectin encompassing the seventh through the RGD-containing tenth type III repeats (FN7–10). The structure reveals an extended rod-like molecule with a long axis of ∼140 Å and highly variable relationships between adjacent domains. An unusually small rotation between domains 9 and 10 creates a distinctive binding site, in which...
The embryo of the flowering plant Arabidopsis develops by a regular pattern of cell divisions and cell shape changes. Mutations in the KNOLLE (KN) gene affect the rate and plane of cell divisions as well as cell morphology, resulting in mutant seedlings with a disturbed radial organization of tissue layers. At the cellular level, mutant embryos are characterized by incomplete cross walls and enlarged...
Ions are not traditionally thought to act as first messengers in signal transduction cascades. However, while searching for genes regulated by the PhoP/PhoQ virulence regulatory system of Salmonella typhimurium, we recovered two loci whose expression is controlled by the concentration of Mg 2+ . To determine whether Mg 2+ is the signal modulating the whole PhoP/PhoQ system, we evaluated...
In higher eukaryotes, Cdk2 kinase plays an essential role in regulating the G1–S transition. Here, we use cycling Xenopus egg extracts to examine the requirement of Cdk2 kinase on progression into mitosis. Interestingly, when Cdk2 kinase activity is inhibited by the Cdk-specific inhibitor, p21 Cip1 , a block to mitosis occurs, and inactive Cdc2–cyclin B accumulates. This block occurs in the...
We describe a novel Xenopus plus end–directed kinesin-like protein (KLP), Xklp2, localized on centrosomes throughout the cell cycle and on spindle pole microtubules during metaphase. Using mitotic spindles assembled in Xenopus egg extracts and different recombinant GST–Xklp2 mutants, we show that this motor is targeted to spindle poles through its C-terminal domain. Xklp2-truncated polypeptides lacking...
We have developed an in vitro motility system from Ascaris sperm, unique amoeboid cells that use filament arrays composed of major sperm protein (MSP) instead of an actin-based apparatus for locomotion. Addition of ATP to sperm extracts induces formation of fibers ∼2 μm in diameter. These fibers display the key features of the MSP cytoskeleton in vivo. Each fiber consists of a meshwork of MSP filaments...
Bacteriophage N4 virion RNA polymerase transcription of double-stranded promoter-containing DNAs requires supercoiled template and E. coli single-stranded DNA–binding protein (EcoSSB); other single-stranded DNA–binding proteins cannot substitute. The DNA determinants of virion RNA polymerase binding at the promoter comprise a small template–strand hairpin. The requirement for EcoSSB is surprising,...
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