The Deletion of the Bre1 Gene in Aspergillus nidulans Impairs Mitotic Growth, Meiosis, and DNA Damage Repair

Bre1 is a homotetrameric E3 ubiquitin-protein ligase that heterodimerizes with Rad6, an E2 ubiquitin-conjugating enzyme, in order to ubiquitinate lysine 123 in Aspergillus nidulans. This post-translational modification promotes methylation of lysines 4 and 79 on histone H3, which are required for certain damage repair pathways and for both optimal mitotic cell growth and meiosis [1-3, 12]. ΔBre1 mutants were generated by exposing protoplasts from strains auxotrophic for pyridoxine to a three-way fusion construct made from the Bre1 5’ and 3’ flanking regions and the Aspergillus fumigatus pyroA gene, which served as a selectable marker. Molecular diagnosis was confirmed via trans-locus PCR. Phenotypic analysis indicates that the loss of Bre1 increases sensitivity to DNA damage agents, decreases mitotic cell growth, and inhibits meiosis. The severe developmental defects of ΔBre1 mutants are consistent with the known roles of Bre1 as an upstream regulator of several important cellular functions. [excerpt

Characterizing He 2 flow through porous materials using counterflow data

Proposed space applications, such as the cooling of infrared and x ray telescopes, have generated substantial interest in the behavior of He(2) flowing in porous materials. For design purposes, classical porous media correlations and room temperature data are often used to obtain order of magnitude estimates of expected pressure drops, while the attendant temperature differences are either ignored or estimated using smooth tube correlations. A more accurate alternative to this procedure is suggested by an empirical extension of the two fluid models. It is shown that four empirical parameters are necessary to describe the pressure and temperature differences induced by He(2) flow through a porous sample. The three parameters required to determine pressure differences are measured in counterflow and found to compare favorably with those for isothermal flow. The fourth parameter, the Gorter-Mellink constant, differs substantially from smooth tube values. It is concluded that parameter values determined from counterflow can be used to predict pressure and temperature differences in a variety of flows to an accuracy of about + or - 20 percent

The influence of microstructure on the tensile behavior of an aluminum metal matrix composite

The relationship between tensile properties and microstructure of a powder metallurgy aluminum alloy, 2009 was examined. The alloy was investigated both unreinforced and reinforced with 15 v/o SiC whiskers or 15 v/o SiC particulate to form a discontinuous metal matrix composite (MMC). The materials were investigated in the as-fabricated condition and in three different hot-rolled sheet thicknesses of 6.35, 3.18, and 1.8 mm. Image analysis was used to characterize the morphology of the reinforcements and their distributions within the matrix alloy. Fractographic examinations revealed that failure was associated with the presence of microstructural inhomogeneities which were related to both the matrix alloy and to the reinforcement. The results from these observations together with the matrix tensile data were used to predict the strengths and moduli of the MMC's using relatively simple models. The whisker MMC could be modeled as a short fiber composite and an attempt was made to model the particulate MMC as a dispersion/dislocation hardened alloy