The invasion-associated type III system of Salmonella typhimurium directs the translocation of Sip proteins into the host cell

The ability of Salmonella typhimurium to interact with host cells is largely dependent on the function of a type III protein-secretion system encoded at centisome 63 of its chromosome. We have shown here that two targets of this protein-secretion system, SipB and SipC, are translocated into cultured intestinal Henle-407 cells. Translocation required the function of the type III secretion apparatus, as an S. typhimurium strain carrying a mutation in invA , which encodes an essential component of this system, failed to translocate the Sip proteins. Null mutations in the genes encoding SipB, SipC or SipD, prevented protein translocation, indicating that these proteins are involved in the translocation process. In contrast, mutations in sipA and sptP , which also encode secreted proteins, did not interfere with the translocation of SipC, indicating that only a subset of targets of the type III secretion system act as translocases. Externally or internally localized bacteria could direct protein translocation into Henle-407 cells as this process occurred in the presence of cytochalasin D at a concentration that prevented bacterial entry, or in the presence of gentamicin added shortly after bacterial internalization at a concentration that killed extracellular Salmonella . These results indicate that protein translocation into host cells may be a universal function of all type III secretion systems.     

The VLF loci, polymorphic between ecotypes Landsberg erecta and Columbia, dissect two branches of phytochrome A signal transduction that correspond to very-low-fluence and high-irradiance responses

Phytochromes play a key role in the perception of light signals by plants. In this study, the three classical phytochrome action modes, i.e. very-low-fluence responses (VLFR), low-fluence responses (LFR) and high-irradiance responses (HIR), were genetically dissected using phyA and phyB mutants of Arabidopsis thaliana (respectively lacking phytochrome A or phytochrome B) and a polymorphism between ecotypes Landsberg erecta and Columbia. Seed germination and potentiation of greening, hypocotyl growth inhibition and cotyledon unfolding in etiolated seedlings of the ecotype Landsberg erecta showed biphasic responses to the calculated proportion of active phytochrome established by one light pulse or repeated light pulses. The first phase, i.e. the VLFR, was absent in the phyA mutant, normal in the phyB mutant (both in the Landsberg erecta background) and severely deficient in Columbia. The second phase, i.e. the LFR, was present in the phyA mutant, deficient in the phyB mutant and normal in Columbia. Under continuous far-red light, HIR of etiolated seedlings were absent in phyA and normal in phyB and Columbia. The segregation of VLFR in recombinant inbred lines derived from a cross between Landsberg erecta and Columbia was analysed by MAPMAKER/QTL. Two quantitative trait loci, one on chromosome 2 ( VLF1 ) and another on chromosome 5 ( VLF2 ), were identified as responsible for the polymorphism. Phytochrome A is proposed to initiate two transduction pathways, VLFR and HIR, involving different cells and/or different molecular steps. This is the first application of the analysis of quantitative trait loci polymorphic between ecotypes to dissect transduction chains of environmental signals.     

Spinalona anophtalma, n. gen. n. sp. (Anomopoda, Chydoridae) a blind epigean cladoceran from the Neovolcanic Province of Mexico

Spinalona anophtalma n. gen. n. sp. is describedon parthenogenetic and ephippial females andmales from material collected in a temporary lagoonlocated in the Neovolcanic Province from Mexico at analtitude of 2507 m above sea level. It ischaracterized by a strong armature of the antenna,postabdomen and postabdominal claw, no compound eyeor ocellus, the exopod of thoracic limb IIIwith only four setae and that of P5 with only three setae.This new taxon has no relationwith blind Alona from hypogean habitats.     

Isolation of K88 Antigen Variants (ab,ac, ad) from Porcine Enterotoxigenic Escherichia coli Belonging to Different Serotypes

Fimbriae isolation by means of thermal shock was applied to fifteen K88-positive (three K88ab, nine K88ac and three K88ad) Escherichia coli reference strains belonging to serotypes O8:K87, O32, O45, O138:K81, O141:K85, O147:K89, O149:K91, and O157, as well as to ten K88-positive enterotoxigenic strains isolated from porcine diarrhea in Spain, all of them belonging to the O149 serogroup. Fimbriae were removed from the bacterial cells by thermal shock at 60 C and then precipitated using ammonium sulfate. The final amount of K88 antigen and the purification degree were not related to the serogroup of the bacteria or to the antigen variant but were related to the buffer used for isolation. Phosphate buffer containing urea was shown to be more effective than Tris-HCl for isolation of K88 antigen. The molecular weights by SDS-PAGE for K88ab, K88ac, and K88ad were 28.5, 29.2, and 31.0 kDa, respectively. All enterotoxigenic E. coli strains isolated in Spain showed the K88ac variant.     

Characterization and regulation of the expression of FatB, an iron transport protein encoded by the pJM1 virulence plasmid

The pJM1-encoded genes fatDCBA are essential for iron acquisition via the siderophore anguibactin. Sequence analysis indicated that the open reading frame corresponding to the fatB gene possesses domains that are characteristic of periplasmic proteins that bind the ferric siderophore. In this work, a monospecific antiserum against an oligopeptide containing the last 27 amino acids of the carboxy-terminal region from this open reading frame was used to demonstrate that fatB encodes a 35 kDa protein that is essential for iron transport. By using this antibody we were able to demonstrate that expression of the fatB gene is negatively regulated by the Fur protein at high iron concentrations. Conversely, its expression was positively regulated by the combined action of the AngR protein and products of the TAF region. FatB, the product of the fatB gene, is isolated with the membrane fraction. In accordance with these findings is the fact that the first 23 amino acid residues of this protein have the properties of a lipoprotein signal sequence. The lipoprotein nature of FatB is supported by the fact that treatment of Vibrio anguillarum cells with globomycin, an inhibitor of the lipoprotein signal peptidase, results in the accumulation of a 38 kDa pro-FatB precursor protein.     

Microscopic anatomy of the ovary ofAlouatta caraya

The microscopic structure of theAlouatta caraya ovary is studied in different ages and reproductive stages. The most significant feature seems to be the presence in adult ovaries of abundant glandular interstitial tissue which occupies both the cortex and medulla. It seems to be derived from the theca interna of atretic follicles. Discrete luteinized masses are present in the medulla in all the ovaries observed. Invaginations of the surface epithelium are seen only in infant and juvenile ovaries. The development of cystic follicles seems to be a common pathway of atresia.     

Lordosis: Inhibiting effects of progesterone in the female rat

Progesterone has two types of inhibitory effects on female sexual behavior that have been well-documented in the guinea pig. The first occurs when high levels of progesterone are present around the start of the estrogen-priming process (“concurrent inhibition”). The second occurs immediately after the display of an estrogen-progesterone-induced period of estrous behavior (“sequential inhibition”). In the present set of experiments, we show that the rat, like the guinea pig, is capable of exhibiting both of these inhibitory effects of progesterone. However, rats require higher doses of progesterone than guinea pigs, at least for concurrent inhibition to be evident. In addition, we show that the dose of progesterone required in a single injection to produce concurrent inhibition is higher than the dose required to produce sequential inhibition in rats. A theory of how progesterone may be accomplishing its inhibitory effects on female sexual behavior in rodents is presented.     

Inducible α-glucosidase of Mucor rouxii: Effects of dimorphism on the development of the wall-bound activity

Some properties of the inducible α-glucosidase system of Mucor rouxii were investigated. This enzymatic activity was induced after resuspending glucose-grown cells in a maltose-supplemented medium. The wall-bound activity of α-glucosidase was determined by using intact cells in the enzymatic assay; this activity represented from 80 to 90% of the total activity present in the induced cells. The addition of glucose before, or during, the induction period repressed α-glucosidase synthesis. α-Glucosidase induction was tested under aerobic and anaerobic conditions. It was found that the enzyme synthesis and the appearance of wall-bound activity were not affected by changing the gaseous environment. On the other hand, it was observed that anaerobically grown yeast-like cells were much less efficient than aerobic mycelia to develop wall-bound α-glucosidase activity. This could explain earlier observations about the incapacity of M. rouxii to utilize maltose as a substrate for anaerobic growth. This idea was strengthened by the fact that, if an anaerobic culture was induced to develop under a mycelial morphology by adding to the medium the chemical agent EDTA, these cells also acquired the capacity to grow on maltose and concomitantly possessed wall-bound α-glucosidase activity. The relevance of the structure of the cell wall on the capacity of M. rouxii to metabolize maltose is discussed.     

An “Inclusion-Body-Like” Configuration of Some Cell Nuclei in Moose

At routine post-mortem of a moose an inclusion-body-like configuration of the nuclei of the cells in the granule layer of the cerebellum was found. This was also observed to a lesser extent in glial cells of the cerebrum, epithelial cells of the collecting tubules of kidney and in the hepatocytes.