Conversion of Ras proteins into an activated GTP-bound state able to bind effector proteins is catalyzed by specific guanine nucleotide exchange factors in response to a large number of extracellular stimuli. Here we report the isolation of mouse cDNAs encoding Ras-GRF2, a multidomain 135-kDa protein containing a COOH-terminal Cdc25-related domain that stimulates release of GDP from Ras but not other GTPases in vitro. Ras-GRF2 bound specifically to immobilized Ras lacking bound nucleotides, suggesting stabilization of the nucleotide-free form of Ras as a mechanism of catalyzing nucleotide exchange. The NH 2 -terminal region of Ras-GRF2 is predicted to contain features common to various signaling proteins including two pleckstrin homology domains and a Dbl homology region. Ras-GRF2 also contains an IQ motif which was required for its apparent constitutive association with calmodulin in epithelial cells ectopically expressing Ras-GRF2. Transient expression of Ras-GRF2 in kidney epithelial cells stimulated GTP binding by Ras and potentiated calcium ionophore-induced activation of mitogen-activated protein kinase (ERK1) dependent upon the IQ motif. Calcium influx caused Ras-GRF2 subcellular localization to change from cytosolic to peripheral, suggesting a possible mechanism for controlling Ras-GRF2 interactions with Ras at the plasma membrane. Epithelial cells overexpressing Ras-GRF2 are morphologically transformed and grow in a disorganized manner with minimal intercellular contacts. Northern analysis indicated a 9-kb GRF2 transcript in brain and lung, where p135 Ras-GRF2 is known to be expressed, and RNAs of 12 kb and 2.2 kb were detected in several tissues. Thus, Ras-GRF2 proteins with different domain structures may be widely expressed and couple diverse extracellular signals to Ras activation.The ras proto-oncogenes encode membrane-bound GTPases that play a central role in the transduction of signals from growth and differentiation factors, immune antigens, and components of the extracellular matrix (33). Ras proteins, and many of the proteins that regulate Ras, have been highly conserved in the course of eukaryotic evolution. Indeed, the fundamental importance of Ras in cellular growth control is underlined by the presence of activated ras alleles in many forms of human cancer (4). Ras GTPases exist in two conformations, cycling between an inactive GDP-bound form and an active GTP-bound state (33). The cyclic interconversion of Ras is controlled by two classes of regulatory proteins: GTPase-activating proteins, which downregulate Ras by stimulating its weak intrinsic GTPase activity, and guanine nucleotide exchange factors (GEFs), which serve to activate Ras by promoting the exchange of bound GDP for GTP. It is through these two classes of regulatory proteins that extracellular signals likely control the activation state and effector protein interactions of Ras.A number of mammalian proteins related in sequence to the Saccharomyces cerevisiae Ras exchange factor encoded by CDC25 have been identified including ...

Nacre, the iridescent material found in pearls and shells of molluscs, is formed through an extraordinary process of matrix-assisted biomineralization. Despite recent advances, many aspects of the biomineralization process and its evolutionary origin remain unknown. The pearl oyster Pinctada fucata martensii is a well-known master of biomineralization, but the molecular mechanisms that underlie its production of shells and pearls are not fully understood. We sequenced the highly polymorphic genome of the pearl oyster and conducted multi-omic and biochemical studies to probe nacre formation. We identified a large set of novel proteins participating in matrix-framework formation, many in expanded families, including components similar to that found in vertebrate bones such as collagen-related VWA-containing proteins, chondroitin sulfotransferases, and regulatory elements. Considering that there are only collagen-based matrices in vertebrate bones and chitin-based matrices in most invertebrate skeletons, the presence of both chitin and elements of collagen-based matrices in nacre suggests that elements of chitin- and collagen-based matrices have deep roots and might be part of an ancient biomineralizing matrix. Our results expand the current shell matrix-framework model and provide new insights into the evolution of diverse biomineralization systems.

WD40 repeat (WDR) domains are protein interaction scaffolds that represent one of the largest protein families in human, and a first WDR inhibitor-an allosteric antagonist of polycomb repressive complex 2-just entered the clinic. A systematic analysis of the CORUM database of protein complexes shows that WDR is the most represented domain in transcriptional regulation and one of the most prevalent in the ubiquitin proteasome system, two pathways of high relevance to drug discovery. Parsing the literature and the vulnerability of cancer cell lines to CRISPR knockout indicates that WDR proteins are targets of interest in oncology and other disease areas. A quantitative analysis of WDR structures reveals that druggable binding pockets can be found on multiple surfaces of these multifaceted protein interaction platforms. These data support the development of chemical probes to further interrogate WDR proteins as an emerging therapeutic target class.

We have determined 222 DNA barcode sequences of 95 fish species in 86 genera of 69 families from 15 orders. Fish were captured by trawl from two important fisheries regions in South China Sea: Spratly Islands (Nansha Islands) and Beibu Gulf. The average genetic distances between intraspecies were about 60-fold less than those of interspecies within different taxonomic levels, as Kimura two-parameter genetic distances averaged 17.260% among congeners, 20.097% among genus, and only 0.317% for intraspecific individuals. There were a few examples of deep divergence within species, suggesting the need for further taxonomic work, and a few examples of closely allied species, perhaps reflecting introgressive hybridization. The results provide further evidence for the reliability and accessibility of DNA barcodes for marine fish identification, and also highlight their effectiveness for flagging cases needing taxonomical reexamination.