Catálogo de publicaciones - revistas

<jats:p> NIH 3T3 fibroblasts stably transformed with a constitutively active isoform of p21 <jats:sup>Ras</jats:sup> , H-Ras <jats:sup>V12</jats:sup> (v-H-Ras or EJ-Ras), produced large amounts of the reactive oxygen species superoxide (·O <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> ). ·O <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> production was suppressed by the expression of dominant negative isoforms of Ras or Rac1, as well as by treatment with a farnesyltransferase inhibitor or with diphenylene iodonium, a flavoprotein inhibitor. The mitogenic activity of cells expressing H-Ras <jats:sup>V12</jats:sup> was inhibited by treatment with the chemical antioxidant <jats:italic>N</jats:italic> -acetyl-L-cysteine. Mitogen-activated protein kinase (MAPK) activity was decreased and c-Jun N-terminal kinase (JNK) was not activated in H-Ras <jats:sup>V12</jats:sup> -transformed cells. Thus, H-Ras <jats:sup>V12</jats:sup> -induced transformation can lead to the production of ·O <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> through one or more pathways involving a flavoprotein and Rac1. The implication of a reactive oxygen species, probably ·O <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> , as a mediator of Ras-induced cell cycle progression independent of MAPK and JNK suggests a possible mechanism for the effects of antioxidants against Ras-induced cellular transformation. </jats:p>

<jats:p> In <jats:italic>Xenopus laevis</jats:italic> embryos, the Wingless/Wnt-1 subclass of Wnt molecules induces axis duplication, whereas the Wnt-5A subclass does not. This difference could be explained by distinct signal transduction pathways or by a lack of one or more Wnt-5A receptors during axis formation. Wnt-5A induced axis duplication and an ectopic Spemann organizer in the presence of hFz5, a member of the Frizzled family of seven-transmembrane receptors. Wnt-5A/hFz5 signaling was antagonized by glycogen synthase kinase-3 and by the amino-terminal ectodomain of hFz5. These results identify hFz5 as a receptor for Wnt-5A. </jats:p>

<jats:p> The bacteriophage N4 single-stranded DNA binding protein (N4SSB) activates transcription by the <jats:italic>Escherichia coli</jats:italic> σ <jats:sup>70</jats:sup> -RNA polymerase at N4 late promoters. Here it is shown that the single-stranded DNA binding activity of N4SSB is not required for transcriptional activation. N4SSB interacts with the carboxyl terminus of the RNA polymerase β′ subunit in a region that is highly conserved in the largest subunits of prokaryotic and eukaryotic RNA polymerases. </jats:p>

<jats:p> Nitrogen regulatory protein C (NtrC) contacts a bacterial RNA polymerase from distant enhancers by means of DNA loops and activates transcription by allowing polymerase to gain access to the template DNA strand. It was shown that NtrC from <jats:italic>Salmonella typhimurium</jats:italic> must build large oligomers to activate transcription. In contrast to eukaryotic enhancer-binding proteins, most of which must bind directly to DNA, some NtrC dimers were bound solely by protein-protein interactions. NtrC oligomers were visualized with scanning force microscopy. Evidence of their functional importance was provided by showing that some inactive non-DNA-binding and DNA-binding mutant forms of NtrC can cooperate to activate transcription. </jats:p>