The WD-repeat protein superfamily in Arabidopsis: conservation and divergence in structure and function

BACKGROUND: The WD motif (also known as the Trp-Asp or WD40 motif) is found in a multitude of eukaryotic proteins involved in a variety of cellular processes. Where studied, repeated WD motifs act as a site for protein-protein interaction, and proteins containing WD repeats (WDRs) are known to serve as platforms for the assembly of protein complexes or mediators of transient interplay among other proteins. In the model plant Arabidopsis thaliana, members of this superfamily are increasingly being recognized as key regulators of plant-specific developmental events. RESULTS: We analyzed the predicted complement of WDR proteins from Arabidopsis, and compared this to those from budding yeast, fruit fly and human to illustrate both conservation and divergence in structure and function. This analysis identified 237 potential Arabidopsis proteins containing four or more recognizable copies of the motif. These were classified into 143 distinct families, 49 of which contained more than one Arabidopsis member. Approximately 113 of these families or individual proteins showed clear homology with WDR proteins from the other eukaryotes analyzed. Where conservation was found, it often extended across all of these organisms, suggesting that many of these proteins are linked to basic cellular mechanisms. The functional characterization of conserved WDR proteins in Arabidopsis reveals that these proteins help adapt basic mechanisms for plant-specific processes. CONCLUSIONS: Our results show that most Arabidopsis WDR proteins are strongly conserved across eukaryotes, including those that have been found to play key roles in plant-specific processes, with diversity in function conferred at least in part by divergence in upstream signaling pathways, downstream regulatory targets and /or structure outside of the WDR regions

Resources, Capabilities and Entrepreneurial Perceptions

We review and develop a subjectivist theory of entrepreneurship that focuses on individuals, their knowledge, resources and skills, and the processes of discovery and creativity, which constitute the heart of entrepreneurship. First, we establish the fundamental importance of subjectivity in entrepreneurial discovery and creativity. Second, we build on Penrose (1959) to elaborate how entrepreneurs' perceptions and personal knowledge shape a firm's "subjective productive opportunity set". Third, we explain that entrepreneurial perceptions and knowledge partly originate from entrepreneurs' experiences in specific business settings such as the firm, the management team, and the industry. Fourth, we highlight the causal connections between subjectivity in entrepreneurship and observed heterogeneity in firm-level economic performance. Lastly, we suggest directions for further advancing a subjectivist resource-based approach to future entrepreneurship research. Copyright Blackwell Publishing Ltd 2007.