Structure of rhodotorucine A, a novel lipopeptide,inducing mating tube formation in Rhodosporidiumtoruloides

Rhodotorucine $\text{A}$ is a peptidyl factor which induces mating tube formation in $\text{Rhodosporidium}\text{toruloides}$. The amino acid sequence of the factor was determined by Edman degradation and enzymatic hydrolysis. Rhodotorucine $\text{A}$ was shown to contain a lipophilic amino acid, S-farnesyl cysteine, at C-terminus by proton magnetic resonance, mass spectrometry and chemical synthesis. We proposed the following structure for rhodotorucine $\text{A}$. H-Tyr-Pro-Glu-Ile-Ser-Trp-Thr-Arg-Asn-Gly-Cys(S-farnesyl)-OH     

Structure and expression of the gene encoding ribosomal protein S1 from the cyanobacterium Synechococcus sp. strain PCC 6301: striking sequence similarity to the chloroplast ribosomal protein CS1

We isolated a 38 kDa ssDNA-binding protein from the unicellular cyanobacterium Synechococcus sp. strain PCC 6301 and determined its N-terminal amino acid sequence. A genomic clone encoding the 38 kDa protein was isolated by using a degenerate oligonucleotide probe based on the amino acid sequence. The nucleotide sequence and predicted amino acid sequence revealed that the 38 kDa protein is 306 amino acids long and homologous to the nuclear-encoded 370 amino acid chloroplast ribosomal protein CS1 of spinach (48% identity), therefore identifying it as ribosomal protein (r-protein) S1. Cyanobacterial and chloroplast S1 proteins differ in size from Escherichia coli r-protein S1 (557 amino acids). This provides an additional evidence that cyanobacteria are closely related to chloroplasts. The Synechococcus gene rps1 encoding S1 is located 1.1 kb downstream from psbB, which encodes the photosystem 11 P680 chlorophyll a apoprotein. An open reading frame encoding a potential protein of 168 amino acids is present between psbB and rps1 and its deduced amino acid sequence is similar to that of E. coli hypothetical 17.2 kDa protein. Northern blot analysis showed that rps1 is transcribed as a monocistronic mRNA.     

In vitro studies on calcium absorption from the gastrointestinal tract in␣small ruminants

Unidirectional flux rates of Ca²⁺ across gastrointestinal tissues from sheep and goats were measured in vitro by applying the Ussing-chamber technique. Except for the sheep duodenum, mucosal to serosal Ca²⁺ flux rates (J _ms) exceeded respective flux rates in the opposite direction (J _sm) in both species and in all segments of the intestinal tract. This resulted in net Ca²⁺ flux rates␣(J _net = J _ms − J _sm) ranging between −2 and 9 nmol · cm⁻² · h⁻¹ in sheep and between 10 and 15 nmol cm⁻² · h⁻¹ in goats. In sheep, only J _net in jejunum, and in goats, J _netin duodenum and jejunum were significantly different from zero. Using sheep rumen wall epithelia, significant J _net of Ca²⁺ of around 5 nmol · cm⁻² · h⁻¹ could be detected. Since the experiments were carried out in the absence of an electrochemical gradient, significant net Ca²⁺ absorption clearly indicates the presence of active mechanisms for Ca²⁺ transport. Dietary Ca depletion caused increased calcitriol plasma concentrations and induced significant stimulations of net Ca²⁺ absorption in goat rumen. J _net of Ca²⁺ across goat rumen epithelia was significantly reduced by 1 mmol · l ⁻¹ verapamil in the mucosal buffer solution. In conclusion, there is clear evidence for the rumen as a main site for active Ca²⁺ absorption in small ruminants. Stimulation of active Ca²⁺ absorption by increased plasma calcitriol levels and inhibition by mucosal verapamil suggest mechanistic and regulatory similarities to active Ca²⁺ transport as described for the upper small intestines of monogastric species. Accepted: 31 July 1996     

STUDIES ON THE MECHANISM OF HAEMOPOIETIC STEM CELL (CFUs) MOBILIZATION

A variety of substances can mobilize haemopoietic stem cells (CFUs) into the peripheral blood. In this study the involvement of the complement system in the mobilization process was investigated. Pretreatment of mice with the complement-activating factor of cobra venom (CoF), which lowered the serum C3 levels to 10–25% of the normal value, could completely prevent CFUs mobilization induced by high doses of CoF, endotoxin (ET) from Salmonella typhosa, inulin, zymosan and the proteolytic enzymes proteinase and trypsin. On the other hand, mobilization induced by the polyanions dextran sulphate and the copolymer of polymethacrylic acid and styrene could not be prevented, or at least affected only slightly. There appears to be a relationship between the extent of decomplementation by CoF and the extent of CFUs mobilization induced by ET. The results indicate that certain agents mobilize CFUs via the complement system, whereas other agents induce CFUs mobilization independent of the availability of complement components.     

Pseudomonas aeruginosa Transmigrates at Epithelial Cell-Cell Junctions,Exploiting Sites of Cell Division and Senescent Cell Extrusion

To achieve systemic infection, bacterial pathogens must overcome the critical and challenging step of transmigration across epithelial barriers. This is particularly true for opportunistic pathogens such as Pseudomonas aeruginosa, an agent which causes nosocomial infections. Despite extensive study, details on the mechanisms used by this bacterium to transmigrate across epithelial tissues, as well as the entry sites it uses, remain speculative. Here, using real-time microscopy and a model epithelial barrier, we show that P. aeruginosa employs a paracellular transmigration route, taking advantage of altered cell-cell junctions at sites of cell division or when senescent cells are expelled from the cell layer. Once a bacterium transmigrates, it is followed by a cohort of bacteria using the same entry point. The basal compartment is then invaded radially from the initial penetration site. Effective transmigration and propagation require type 4 pili, the type 3 secretion system (T3SS) and a flagellum, although flagellum-deficient bacteria can occasionally invade the basal compartment from wounded areas. In the basal compartment, the bacteria inject the T3SS toxins into host cells, disrupting the cytoskeleton and focal contacts to allow their progression under the cells. Thus, P. aeruginosa exploits intrinsic host cell processes to breach the epithelium and invade the subcellular compartment.