Cell polarization requires that a cellular axis or cell-surface site be chosen and that the cytoskeleton be organized with respect to it. Details of the link between the cytoskeleton and the chosen axis or site are not clear. Cells of the yeast Saccharomyces cerevisiae exhibit cell polarization in two phases of their life cycle, during vegetative growth and during mating, which reflects responses to intracellular and extracellular signals, respectively. Here we describe the isolation of two mutants defective specifically in cell polarization in response to peptide mating pheromones. The mutants carry special alleles (denoted bem1-s) of the BEM1 gene required for cell polarization during vegetative growth. Unlike other bem1 mutants, the bem1-s mutants are normal for vegetative growth. Complete deletion of BEM1 leads to the defect in polarization of vegetative cells seen in bem1 mutants. The predicted sequence of the BEM1 protein (Bem1p) reveals two copies of a domain (denoted SH3) that is found in many proteins associated with the cortical cytoskeleton and which may mediate binding to actin or some other component of the cell cortex. The sequence of Bem1p and the properties of mutants defective in this protein indicate that it may link the cytoskeleton to morphogenetic determinants on the cell surface.

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Cells of the yeast S. cerevisiae choose bud sites in an axial or bipolar spatial pattern depending on their cell type. We have identified a gene, BUD5, that resembles BUD1 and BUD2 in being required for both patterns; bud5- mutants also exhibit random budding in all cell types. The BUD5 nucleotide sequence predicts a protein of 538 amino acids that has similarity to the S. cerevisiae CDC25 product, an activator of RAS proteins that catalyzes GDP-GTP exchange. Two potential targets of BUD5 are known: BUD1 (RSR1) and CDC42, proteins involved in bud site selection and bud formation, respectively, that have extensive similarity to RAS. We also show that BUD5 interacts functionally with a gene, BEM1, that is required for bud formation. This interaction provides further support for the view that products involved in bud site selection guide the positioning of a complex necessary for bud formation.

Abstract. Dystrophin plays an important role in skeletal muscle by linking the cytoskeleton and the extracellular matrix. The amino terminus of dystrophin binds to actin and possibly other components of the subsarcolemmal cytoskeleton, while the carboxy terminus associates with a group of integral and peripheral membrane proteins and glycoproteins that are collectively known as the dystrophin-associated protein (DAP) complex. We have generated transgenic/mdx mice expressing "full-length" dystrophin constructs, but with consecutive deletions within the COOH-terminal domains. These mice have enabled analysis of the interaction between dystrophin and members of the DAP complex and the effects that perturbing these associations have on the dystrophic process. Deletions within the cysteine-rich region disrupt the interaction between dystrophin and the DAP complex, leading to a severe dystrophic pathology. These deletions remove the [3-dystroglycan-binding site, which leads to a parallel loss of both [3-dystroglycan and the sarcoglycan complex from the sarcolemma. In contrast, deletion of the alternatively spliced domain and the extreme COOH terminus has no apparent effect on the function of dystrophin when expressed at normal levels. The proteins resulting from these latter two deletions supported formation of a completely normal DAP complex, and their expression was associated with normal muscle morphology in mdx mice. These data indicate that the cysteine-rich domain is critical for functional activity, presumably by mediating a direct interaction with [3-dystroglycan. However, the remainder of the COOH terminus is not required for assembly of the DAP complex.UCHENNE muscular dystrophy (DMD) 1 and the milder Becker muscular dystrophy (BMD) are caused by mutations in the dystrophin gene (24). Although dystrophin is expressed from a variety of promoters in a wide array of tissues, disruption of dystrophin function in striated muscle leads to the most devastating effects of these diseases (for review see reference 2). The complete function of the dystrophin protein in skeletal muscle has not yet been fully elucidated, although it is thought to provide a crucial link between the intracellular actin cytoskeleton and the extracellular matrix (15). The mdx mouse contains a nonsense mutation in the dystrophin gene that leads to a complete absence of dystrophin in muscle, which causes a similar muscle degeneration as is Address all correspondence to J.S. Chamberlain, Department of Human Genetics, University of Michigan Medical School, Ann Arbor, MI 48109. Tel.: (313) 763-4171; Fax: (313) 763-3784. The current address for Gregory A. Cox is The Jackson Laboratories, 600 Main Street, Bar Harbor, ME 04609. Abbreviations used in this paper:BMD, Becker muscular dystrophy; DAP, dystrophin-associated protein; DMD, Duchenne muscular dystrophy; GMA, glycol methacrylate; LGMD, limb girdle muscular dystrophy. seen in DMD patients. As a result, the mdx mouse is a useful system for studying the function of the dystrophin protein.The full...

We report a large compilation of the internal validations of the probabilistic genotyping software STRmix™. Thirty one laboratories contributed data resulting in 2825 mixtures comprising three to six donors and a wide range of multiplex, equipment, mixture proportions and templates. Previously reported trends in the LR were confirmed including less discriminatory LRs occurring both for donors and non-donors at low template (for the donor in question) and at high contributor number. We were unable to isolate an effect of allelic sharing. Any apparent effect appears to be largely confounded with increased contributor number.