Cell adhesion molecule in the hexactinellid Aphrocallistes vastus

Abstract. The Hexactinellida sponge Aphrocallistes vastus contains a soluble aggregation factor (AF) whose purification has been described in this communication. It is characterized by a S°_20.w value of 37 and a buoyant density of 1.45 g/cm³. The AF is a glycoporteinaceous particle composed of three major protein species; no core structure could be visualized. In the presence of Ca²⁺, the AF causes secondary aggregation of single cells. The aggregation process is temperature, pH, and ionic strength independent within a broad range. Evidence is presented indicating that two (or more) AF molecules are required for the establishment of a stable cell: cell interaction. In contrast to the AFs from demosponges, the hexactinellid AF functions species-unspecifically.     

Metabolism of some carcinogenic aromatic amines in four species of marine sponges

Postmitochondrial fractions from marine sponges Geodia cydonium, Tethya aurantium, Verongia aerophoba and Pellina semitubulosa activate precarcinogenic aromatic amine 2-aminoanthracene, but not precarcinogenic polycyclic aromatic hydrocarbon benzo(a)pyrene, to Salmonella typhimurium TA 98 mutagens. All four sponge species lack a benzo(a)pyrene monooxygenase activity, but possesses the enzyme activity whose characteristics (selective activation of aromatic amines, NADPH-dependency, pH optimum at 8.4) are similar to FAD-containing monooxygenase. Tethya postmitochondrial fraction possesses an UDP-glucuronyl transferase activity which catalyzes the conjugation of a considerable part of metabolized 2-acetylamino [9-14C]fluorene to water soluble glucuronides. The possible ecological significance of exuded aromatic amine metabolites as well as the significance of the presence of the selective potential for the activation of aromatic amines to mutagens among sponges for our understanding of the fate and effects of carcinogens in the marine environment are discussed.     

Characterization of the DNA binding domain of bacteriophage lambda O protein

The lambda O and P gene products are required for the initiation of lambda DNA replication. In order to study the biochemistry of this process, we have constructed plasmids that carry the lambda O gene, P gene, and half of the O gene coding for the amino-terminal half of the O protein. Each is under the control of the inducible lambda promoter, PL. We have purified these three proteins from induced cells carrying the plasmids. Our results show that the amino-terminal portion of the O protein binds to the lambda origin of replication in a manner similar to the intact lambda O protein, demonstrating that the amino-terminal portion of O protein contains the DNA binding domain. Using chromatographic procedures, we have isolated a complex of lambda O and P proteins with lambda dv DNA. The amino-terminal portion of the O protein does not complex with P protein under the same conditions. This suggests that the specificity of the lambda O protein for P protein resides in the carboxyl-terminal half of the lambda O protein. Our results also show that, while the intact O protein is active in in vitro replication of lambda dv plasmid DNA, the amino-terminal portion of the O protein is inactive and is a competitive inhibitor of the lambda O protein in this reaction. These results confirm previous genetic observations that were interpreted as indicating a bifunctional structure for the lambda O protein with the amino-terminal domain recognizing the lambda origin of replication and the carboxyl-terminal domain interacting with the lambda P protein.     

Identification and isolation of the primary aggregation factor from the cell membrane of the sponge Geodia cydonium

Summary The primary aggregation factor (pAF) of sponge cells is a glycoprotein that is firmly associated with the cell membrane. Polyspecific antibodies (anti-GM) prepared from sera raised against membranes of cells from the siliceous sponge Geodia cydonium were found to inhibit initial aggregation of homologous cells. The inhibition of aggregation, caused by anti-GM was neutralized by pAF. The pAF had been successfully solubilized and enriched by affinity chromatography, gel filtration and density gradient centrifugation, if checked by polyacrylamide gel electrophoresis in the presence of urea. The M_r of the native pAF was approximately 40 000 as estimated by gel filtration; under denaturing conditions three protein species (M_r: 16 500, 15 500 and 13 500) were identified in the pAF preparation. The pAF was precipitable by Ca⁺⁺ and did not cross-react with antisera against homologous purified secondary aggregation factor and lectin. It is mainly composed of protein (48.0%) and carbohydrate (50.2%). The isolated pAF restored the aggregation potency not only of factor-depleted Geodia cells but also of cells from other Demospongiae. However, the pAF displayed no aggregation enhancing effect on urea-treated cells from species belonging to the Calcispongiae or Hexactinellida. We hypothesize that in contrast to the secondary aggregation, the initial aggregation of Geodia cells is mediated by the one-component system, the bivalent and bifunctional pAF.     

Protein synthesis of the sponge Geodia cydonium: characterization of the system

The ribosomal population of the sponge Geodia cydonium has been examined. The monosomes have a sedimentation constant of 80 S, the sizes of the subunits are approximately 60 S and 45 S respectively. The polyribosomes contain up to 40 ribosomal units. Cell free protein synthesizing systems (cell homogenate as well as reconstituted system) have been prepared and characterized with respect to Mg²⁺, KCI and ATP concentrations, temperature, pH and time course of the reaction. In the cell-free system and in the cellular system the protein biosynthesis is inhibited by chloramphenicol. It is not affected by cycloheximide.     

Buchbesprechungen

Ohne Zusammenfassung     

Modulation of lambda integrase synthesis by rare arginine tRNA

Lambda's int gene contains an anomalously high frequency of the rare arginine codons AGA and AGG when compared to genes of Escherichia coli or to the rest of phage lambda. These are the least frequent codons in genes of E. coli and are recognized by the rarest tRNAs. The presence of these codons reduces the translation rate and, depending on the context, this can strongly modulate translational efficiency by a variety of mechanisms. In this study, we show that expression of the natural int gene may also be modulated by rare arginine codon usage, and we explore this mechanism.     

An Ustilago maydis Mutant Partially Blocked in P45014DM Activity Is Hypersensitive to Azole Fungicides

An Ustilago maydis ergosterol biosynthesis mutant (A14) which is partially blocked in sterol 14alpha-demethylase (P45014DM) activity is described. This mutant accumulated the abnormal 14alpha-methyl sterols, eburicol, 14alpha-methylfecosterol, and obtusifoliol, along with significant amounts of ergosterol. Although the A14 mutant grew nearly as well as the wild type, it was impaired in cell extension growth, which indicated a dysfunction in apical cell wall synthesis. The mutant was also found to be hypersensitive to the azole fungicides penconazole and tebuconazole.