Mutations which affect the inhibition of protein phosphatase 2A by simian virus 40 small-t antigen in vitro decrease viral transformation.

Three independent point mutations within residues 97 to 103 of the simian virus 40-small-t antigen (small-t) greatly reduced the ability of purified small-t to inhibit protein phosphatase 2A in vitro. These mutations affected the interaction of small-t antigen with the protein phosphatase 2A A subunit translated in vitro, and a peptide from the region identified by these mutations released the A subunit from immune complexes. When introduced into virus, the mutations eliminated the ability of small-t to enhance viral transformation of growth-arrested rat F111 cells. In contrast, the mutant small-t antigens were unimpaired in the transactivation of the adenovirus E2 promoter, an activity which was reduced by a double mutation in small-t residues 43 and 45.     

Platelet activating factor synthesis and metabolism in intestinal ischaemia-reperfusion injury

The object of this study was to characterize the synthesis and metabolism of platelet activating factor (PAF) by intestinal mucosa subjected to ischaemia-reperfusion injury. Canine intestinal mucosa produced 16:0-PAF, 18:0-PAF, and high levels of the corresponding lyso- PAF metabolites. Three h of intestinal ischaemia and ischaemia followed by 1 h of reperfusion did not affect the synthesis or metabolism of PAF by intestinal mucosa. Intestinal mucosa elaborated a factor that rapidly hydrolyzes PAF to lyso-PAF. The observed hydrolysis rate was not altered by ischaemia or ischaemia and reperfusion. In conclusion, this study suggests that intestinal mucosa produces PAF and rapidly hydrolyzes PAF. The PAF synthesis and metabolism rates of intestinal mucosa is not altered by ischaemia reperfusion in this model under the imposed conditions.     

Crystallization and preliminary crystallographic studies of the precursor and mature forms of a neutral lipase from the fungus Rhizopus delemar

A neutral lipase from the filamentous fungus Rhizopus delemar has been crystallized in both its proenzyme and mature forms. Although the latter crystallizes readily and produces a variety of crystal forms, only one was found to be suitable for X-ray studies. It is monoclinic (C2, a = 92.8 Å, b = 128.9 Å, c = 78.3 Å, β = 135.8) with two molecules in the asymmetric unit related by a noncrystallographic diad. The prolipase crystals are orthorhombic (P2₁2₁2₁, with a = 79.8 Å, b = 115.2 Å, c = 73.0 Å) and also contain a pair of molecules in the asymmetric unit. Initial results of molecular replacement calculations using the refined coordinates of the related lipase from Rhizomucor miehei identified the correct orientations and positions of the protein molecules in the unit cells of crystals of both proenzyme and the mature form. © 1994 John Wiley & Sons, Inc.     

ThePenicillium chrysogenum andAspergillus nidulans wetA developmental regulatory genes are functionally equivalent

Aspergillus nidulans andPenicillium chrysogenum are related fungi that reproduce asexually by forming multicellular conidiophores and uninucleate conidia. InA. nidulans, spore maturation is controlled by thewetA (AwetA) regulatory gene. We cloned a homologous gene (PwetA) fromP. chrysogenum to determine if spore maturation is regulated by a similar mechanism in this species. ThePwetA andAwetA genes are similar in structure and functional organization. The inferred polypeptides share 77% overall amino acid sequence similarity, with several regions having > 85% similarity. The genes also had significant, local sequence similarities in their 5′ flanking regions, including conserved binding sites for the product of the regulatory geneabaA.PwetA fully complemented anA. nidulans wetA deletion mutation, demonstrating thatPwetA and its 5′ regulatory sequences function normally inA. nidulans. These results indicate that the mechanisms controlling sporulation inA. nidulans andP. chrysogenum are evolutionarily conserved.     

Inhibition of EGF-Induced Signal Transduction by Microgravity Is Independent of EGF Receptor Redistribution in the Plasma Membrane of Human A431 Cells

Epidermal growth factor (EGF)-induced c-fos and c-jun expression is strongly suppressed in microgravity. We investigate here whether this is due to inhibition of processes occurring during the initiation of EGF-induced signal transduction. For this purpose, EGF-induced receptor clustering is used as a marker. The lateral distribution of EGF receptors is directly visualized at an ultrastructural level by the label-fracture method. Quantification of the receptor distributions shows that EGF-induced receptor redistribution is similar under normal and microgravity conditions. This suggests that microgravity influences EGF-induced signal transduction downstream of EGF binding and EGF receptor redistribution, but upstream of early gene expression in human A431 cells.     

Intragenic Dominant Suppressors of Glp-1, a Gene Essential for Cell-Signaling in Caenorhabditis Elegans, Support a Role for Cdc10/Sw16/Ankyrin Motifs in Glp-1 Function

The glp-1 gene product mediates cell-cell interactions required for cell fate specification during development in Caenorhabditis elegans. To identify genes that interact with glp-1, we screened for dominant suppressors of two temperature-sensitive glp-1 alleles and recovered 18 mutations that suppress both germline and embryonic glp-1 phenotypes. These dominant suppressors are tightly linked to glp-1 and do not bypass the requirement for a distal tip cell, which is thought to be the source of a signal that is received and transduced by the GLP-1 protein. Using single-strand conformation polymorphism (SSCP) analysis and DNA sequencing, we found that at least 17 suppressors are second-site intragenic revertants. The suppressors, like the original glp-1(ts) mutations, are all located in the cdc10/SWI6/ankyrin domain of GLP-1. cdc10/SWI6/ankyrin motifs have been shown to mediate specific protein-protein interactions in other polypeptides. We propose that the glp-1(ts) mutations disrupt contact between GLP-1 and an as yet unidentified target protein(s) and that the dominant suppressor mutations restore appropriate protein-protein interactions.     

Polysulfide as a possible substrate for sulfur-reducing bacteria

Because of its low solubility it is unlikely that elemental sulfur serves as the direct substrate for sulfur-reducing bacteria. To test the hypothesis that polysulfide may represent a soluble intermediate of sulfur reduction, the maximal polysulfide concentrations formed from elemental sulfur in aqueous sulfide solutions were measured at near neutral pH and at temperatures up to 90°C. The saturation concentrations decreased by two orders of magnitude when the pH was lowered from 7 to 6 at a given temperature, and increased about tenfold when the temperature was raised from 37°C to 90°C at a given pH. The dissolution of 0.1 mM zerovalent sulfur in 1 mM sulfide (H₂S+HS^–) required a pH of 7.5 at 20°C and of only 6.1 at 100°C. A comparison with the growth optima of sulfur-reducers suggests that polysulfide is present at sufficient concentration at the growth conditions of the Bacteria and the moderately acidophilic Archaea. Polysulfide is apparently not available at the growth conditions of the extremely acidophilic Archaea. Alternative mechanisms for the sulfur utilization under these conditions are discussed.Abbreviations MOPS Morpholinopropanesulfonate - PIPES 1,4 piperazine-N,N-bis(2-ethanesulfonate) - HEPES N-2-hydroxy-ethylpiperazine-N-ethanesulfonate