Two independent type III secretion mechanisms for YopE in Yersinia enterocolitica

Pathogenic Yersinia species escape the infected host's defense mechanisms by targeting cytotoxic Yop proteins into the cytoplasm of macrophages via a type III secretion pathway. Two separate secretion signals contained in YopE were identified, each of which were sufficient but not necessary for the secretion of reporter molecules. One signal is located within the coding sequence of the first 15 amino acids and is sufficient for the secretion of fusion proteins but not required for YopE secretion. The second signal is located downstream at residues 15–100 of YopE and is only recognized by the type III machinery when it is bound to SycE. We propose the existence of two independent mechanisms that allow for the secretion of Yop proteins.     

Regulation of O-antigen chain length is required for Shigella flexneri virulence

It is shown that Shigella flexneri maintains genetic control over the modal chain length of the O-antigen polysaccharide chains of its lipopolysaccharide (LPS) molecules because such a distribution is required for virulence. The effect of altering O-antigen chain length on S. flexneri virulence was investigated by inserting a kanamycin (Km)-resistance cassette into the rol gene (controlling the modal O-antigen chain length distribution), and into the rfbD gene, whose product is needed for synthesis of dTDP-rhamnose (the precursor of rhamnose in the O-antigen). The mutations had the expected effect on LPS structure. The rol ::Km mutation was impaired in the ability to elicit keratoconjunctivitis, as determined by the Serény test. The rol ::Km and rfbD ::Km mutations prevented plaque formation on HeLa cells, but neither mutation affected the ability of S. flexneri to invade and replicate in HeLa cells. Microscopy of bacteria-infected HeLa cells stained with fluorescein isothiocyanate (FITC)-phalloidin demonstrated that both the rol ::Km and rfbD ::Km mutants were defective in F-actin tail formation: the latter mutant showed distorted F-actin tails. Plasma-membrane protrusions were occasionally observed. Investigation of the location of IcsA (required for F-actin tail formation) on the cell surface by immunofluorescence and immunogold electron microscopy showed that while most rol mutant bacteria produced little or no cell-surface IcsA, 10% resembled the parental bacterial cell (which had IcsA at one cell pole; the rfbD mutant had IcsA located over its entire cell surface although it was more concentrated at one end of the cell). That the O-antigen chains of the rol ::Km mutant did not mask the IcsA protein was demonstrated by using the endorhamnosidase activity of Sf6c phage to digest the O-antigen chains, and comparing untreated and Sf6c-treated cells by immunofluorescence with anti-IcsA serum.     

Production of neosolaniol byFusarium tumidum

Extracts from autoclaved maize culture ofFusarium tumidum strain R-5823 were toxic towardsArtemia salina. Bioassay-guided fractionation of the organic extract led to the isolation of the toxic compound that was identified as the trichothecene toxin neosolaniol (NEOS) by¹H,¹³C nuclear magnetic resonance spectroscopy and low-resolution electronic impact mass spectrometry. The amount of NEOS produced by the strain R-5823 was 300 mg/kg maize culture. NEOS was also detected by HPLC in cultures of four out of seven additional strains ofF. tumidum andGibberella tumida with different origin, in amounts ranging from 1 to 311 mg/kg. This is the first report on the production of a trichothecene toxin byF. tumidum.     

Partial deletion of 4p16 band in a ring chromosome and wolf syndrome

Summary A new case of ring chromosome 4 in a 2-day-old female child with multiple malformations is described. By means of the GTG-banding technique, a karyotype 46,XX,r(4), (p16q35) was determined. The characteristics of the child's karyotype and the relationship with the structure of the chromosome, especially the location of the deletion that produces the syndrome, are compared with previous reports.     

Steroid modulation of oxytocin/vasopressin receptors in the uterus

Oxytocin (OT) and V1 vasopressin (VP) receptors are present simultaneously in several tissues, including the uterus. In myometrium these receptors mediate contractility, while in endometrium they mediate the release of other uterotonic substances as endothelin (ET). In rabbit myometrium, estrogens increase, while progesterone blunts neurohypophysial hormone receptors. However, the action of sex steroids on OT and V1 VP receptors differs in terms of the ED₅₀ and maximal effect. Therefore, at parturition, only OT receptors show a dramatic rise, while V1 VP receptors do not change, suggesting a major role for OT in labor. ET is a potent stimulator of uterine activity acting through specific receptors present on myometrial cells. These receptors as well as the endometrial localization of ET are modulated by sex steroids, indicating that ET might represent a paracrine regulator of uterine activity. In humans, OT but not V1 VP receptors increase as pregnancy progresses, confirming the primary relevance of OT in timing delivery.     

Specificity of Zea mays histone deacetylase is regulated by phosphorylation.

Mono Q ion exchange high performance liquid chromatography (HPLC) reveals that the main histone deacetylase activity (HD1) of germinating Zea mays embryos consists of multiple enzyme forms. Chromatography of HD1 after treatment with alkaline phosphatase yields two distinct histone deacetylase forms (HD1-A, HD1-B). The same is true for chromatography after phosphatase treatment of a total cell extract. One of these enzyme forms (HD1-A) is subject to phosphorylation, which causes a change in the substrate specificity of the enzyme, as shown with HPLC-purified individual core histone species; the substrate specificity for H2A increases more than 2-fold after phosphorylation, whereas the specificity for H3 decreases to about 60%. The total histone deacetylase activity is quantitatively released from isolated nuclei after extraction with moderate ionic strength buffers; no significant residual enzyme activity could be detected in the nuclear matrix.