Identification of non-catalytic conserved regions in xylanases encoded by the xynB and xynD genes of the cellulolytic rumen anaerobe Ruminococcus flavefaciens

xynB is one of at least four genes from the cellulolytic rumen anaerobe Ruminococcus flavefaciens 17 that encode xylanase activity. The xynB gene is predicted to encode a 781-amino acid product starting with a signal peptide, followed by an amino-terminal xylanase domain which is identical at 89% and 78% of residues, respectively, to the amino-terminal xylanase domains of the bifunctional XynD and XynA enzymes from the same organism. Two separate regions within the carboxy-terminal 537 amino acids of XynB also show close similarities with domain B of XynD. These regions show no significant homology with cellulose- or xylan-binding domains from other species, or with any other sequences, and their functions are unknown. In addition a 30 to 32-residue threonine-rich region is present in both XynD and XynB. Codon usage shows a consistent pattern of bias in the three xylanase genes from R. flavefaciens that have been sequenced.     

Nuclear size and DNA content of the embryo and endosperm during their initial stages of development in Glycine max (Fabaceae)

A technique was developed for isolating embryo sacs from ovules of soybean and for separating embryo from endosperm. Image analysis and cytophotometry were used to determine the relative mass of DNA and size of nuclei of endosperm and embryo cells. Analyses were done at the globular through late heart-shaped embryo stages to correlate ploidy level or nuclear size, and differentiation in these tissues. Mean size of embryo nuclei was fairly constant through all stages studied. Ploidy condition of the embryo was stable, 95%–99% of the nuclei were distributed in a bipolar pattern by relative mass at 2C and 4C. Few embryo nuclei (3%) had ploidy levels above 4C at the late heart-shaped embryo stage. Variability in size of endosperm nuclei seemed correlated with the morphological state of these nuclei (free-nuclear vs. cellular). Most endosperm cells did not show significant polyploidy with 84%–92% of nuclei in the expected 3C–6C range, but some nuclei with elevated ploidy levels were noted during endosperm cellularization. Endosperm senescence was correlated with nuclear DNA loss over time. Polyploidy seems to have no direct role in the early differentiation of the soybean embryo and endosperm, but these stable conditions may be necessary for the early establishment of the embryo.     

Stereochemistry of residues in turning regions of helical proteins

JBIC Journal of Biological Inorganic Chemistry - We have developed a geometrical approach to quantify differences in the stereochemistry of α-helical and turning regions in four iron proteins....     

Ultraviolet radiation inhibits human natural killer activity and lymphocyte proliferation

Exposure to ultraviolet radiation (UVR) has been implicated in the predisposition to certain neoplasms and leads to viral reactivation. Natural killer (NK) activity may play a role in immunosurveillance and response to certain viral infections. We have evaluated the sensitivity to UVR of human NK activity, a nonproliferative function, and the proliferative response to the mitogen phytohemagglutinin (PHA). In vitro exposure to UVR resulted in a dose-dependent inhibition of NK activity and response to PHA. The wavelength dependence for UVR inhibition of NK activity and of the PHA response of lymphocytes were virtually superimposable at wavelengths at or above 300 nm, but NK activity was less sensitive to UVR at 260 and 280 nm. Maximal sensitivity for both functions was found at 260 nm, consistent with a nucleic acid chromophore mediating UVR inhibition of both activities. The DNA-directed drugs mitomycin C, acridine orange, and adriamycin at concentrations that inhibit proliferation are poor inhibitors of NK activity. These results suggest that UVR inhibition of NK activity as well as proliferation may be mediated by a nucleic acid chromophore. NK activity, however, is less sensitive to direct damage of DNA by alkylation, distortion, or oxidation. At 300 nm, the amount of radiation required to inhibit NK activity and proliferation is within the range penetrating to the dermis and capillaries during environmental exposure to sunlight.