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741.
742.
Doubly uniparental inheritance (DUI) provides an intriguing system for addressing aspects of molecular evolution and intermolecular recombination of mitochondrial DNA. For this reason, a large sequence analysis has been performed on Tapes philippinarum (Bivalvia, Veneridae), which has mitochondrial DNA heteroplasmy that is consistent with a DUI. The sequences of a 9.2-kb region (containing 29 genes) from 9 individuals and the sequences of a single gene from another 44 individuals are analyzed. Comparisons suggest that the two sex-related mitochondrial genomes do not experience a neutral pattern of divergence and that selection may act with varying strength on different genes. This pattern of evolution may be related to the long, separate history of M and F genomes within their tissue-specific "arenas." Moreover, our data suggest that recombinants, although occurring in soma, may seldom be transmitted to progeny in T. philippinarum. 相似文献
743.
Antifungal activity of phenyllactic acid against molds isolated from bakery products 总被引:8,自引:0,他引:8
Phenyllactic acid (PLA) has recently been found in cultures of Lactobacillus plantarum that show antifungal activity in sourdough breads. The fungicidal activity of PLA and growth inhibition by PLA were evaluated by using a microdilution test and 23 fungal strains belonging to 14 species of Aspergillus, Penicillium, and Fusarium that were isolated from bakery products, flours, or cereals. Less than 7.5 mg of PLA ml(-1) was required to obtain 90% growth inhibition for all strains, while fungicidal activity against 19 strains was shown by PLA at levels of < or = 10 mg ml(-1). Levels of growth inhibition of 50 to 92.4% were observed for all fungal strains after incubation for 3 days in the presence of 7.5 mg of PLA ml(-1) in buffered medium at pH 4, which is a condition more similar to those in real food systems. Under these experimental conditions PLA caused an unpredictable delaying effect that was more than 2 days long for 12 strains, including some mycotoxigenic strains of Penicillium verrucosum and Penicillium citrinum and a strain of Penicillium roqueforti (the most widespread contaminant of bakery products); a growth delay of about 2 days was observed for seven other strains. The effect of pH on the inhibitory activity of PLA and the combined effects of the major organic acids produced by lactic acid bacteria isolated from sourdough bread (PLA, lactic acid, and acetic acid) were also investigated. The ability of PLA to act as a fungicide and delay the growth of a variety of fungal contaminants provides new perspectives for possibly using this natural antimicrobial compound to control fungal contaminants and extend the shelf lives of foods and/or feedstuffs. 相似文献
744.
Spitz F Montavon T Monso-Hinard C Morris M Ventruto ML Antonarakis S Ventruto V Duboule D 《Genomics》2002,79(4):493-498
Mesomelic dysplasia is a severe shortening of forearms and forelegs, and is found in several distinct human syndromes. Here, we report the cloning of the breakpoints of a human t(2;8)(q31;p21) balanced translocation associated with mesomelic dysplasia of the upper limbs, as well as with vertebral defects. We show that this translocation does not disrupt any gene, hence it most likely exerts its deleterious effect by modifying gene regulation. The HOXD complex lies approximately 60 kb from the translocation breakpoint on chromosome 2. This cluster of genes has an important role in the development of both the vertebral column and the limbs. Only a few cases of mutations of these homeotic genes have been described so far in humans. However, gain- and loss-of-function of Hoxd genes in mice can induce mesomelic dysplasia-like phenotypes, suggesting that misexpression of HOXD genes may indeed be at the origin of this hereditary phenotype. 相似文献
745.
Cooperative interactions within ion-pair networks of hyperthermostable proteins are thought to be a major determinant for extreme protein stability. While the favorable thermodynamic contributions of optimized electrostatics in general as well as those of pairwise interactions have been documented, cooperativity between pairwise interactions has not yet been studied thermodynamically in proteins from hyperthermophiles. In this study we use the isolated cofactor binding domain of glutamate dehydrogenase from the hyperthermophilic bacterium Thermotoga maritima to analyze pairwise and cooperative interactions within the salt-bridge triad Arg190-Glu231-Lys193. The X-ray structure of the domain was solved at 1.43 A and reveals the salt-bridge network with surrounding solvent molecules in detail. All three participating charges in the network were mutated to alanine in all combinations. The X-ray structure of the variant lacking all three charges reveals that the removal of the side chains has no effect on the overall conformation of the protein. Using solvent denaturation and thermodynamic cycles, the interaction energies between each pair of residues in the network were determined in the presence and in the absence of the third residue. Both the Arg190-Glu231 ion pair and the Lys193-Glu231 salt bridge in the absence of the third residue, contribute favorably to the free energy for unfolding of the domain in urea. Using guanidinium chloride as denaturant reveals a strong cooperativity between the two ion-pair interactions, the presence of the second ion pair converts the first interaction from destabilizing into stabilizing by as much as 1.09 kcal/mol. The different energetics of the salt-bridge triad in urea and GdmCl are discussed with reference to the observed anion binding in the crystal structure at high ionic strength and their possible role in a highly charged, high-temperature environment such as the cytoplasm of hyperthermophiles. 相似文献
746.
The sciatic nerve, and the Schwann cells in particular, are able to synthesize progesterone and possess the enzymes forming the 5alpha-reduced and the 3alpha-5alpha-reduced derivatives of progesterone: dihydroprogesterone and tetrahydroprogesterone. Moreover, the progesterone receptor (PR) is present in the sciatic nerve and in Schwann cell cultures. These facts suggest that progesterone and its derivatives might play a role in the control of the synthesis of the two major proteins of the peripheral nervous system (PNS): the glycoprotein Po (Po) and peripheral myelin protein 22 (PMP22). We have shown that: (a) dihydroprogesterone enhances the low mRNA levels of Po in the sciatic nerve of aged male rats; (b) progesterone and its derivatives stimulate the gene expression of Po in the sciatic nerve of adult rats and in Schwann cell cultures; (c) tetrahydroprogesterone increases PMP22 gene expression in the sciatic nerve of adult rats and in Schwann cell cultures. In additional experiments, utilizing agonists and antagonists of PR and GABAA receptor, we have observed that progesterone and its derivatives control Po gene expression via the PR, while tetrahydroprogesterone modulates the expression of PMP22 through the GABAA receptor. 相似文献
747.
Polycomb,epigenomes, and control of cell identity 总被引:28,自引:0,他引:28
748.
Diarrhoeagenic Escherichia coli strains of serotype O111:H12 are characterized by their aggregative pattern of adherence on cultured epithelial cells and thus are considered enteroaggregative E. coli (EAEC). We have previously shown that these EAEC strains lack the genes encoding the aggregative fimbriae I and II described in other heterologous EAEC strains. In this paper, we show compelling data suggesting that a plasmid-encoded outer membrane 58 kDa protein termed aggregative protein 58 (Ap58) produced by EAEC O111:H12 strains, is associated with the adherence capabilities and haemagglutination of animal red blood cells. This conclusion is supported by several lines of evidence: (i) adherent O111:H12 strains are able to produce Ap58; (ii) non-adherent O111:H12 strains are unable to produce Ap58; (iii) antibodies raised against Ap58 inhibited adherence and haemagglutination of epithelial and bovine red blood cells, respectively; (iv) a non-adherent E. coli K-12 host strain containing the ap58 gene determinant on plasmid pVM15 displayed abundant adherence to cultured HEp-2 cells; and (v) the purified Ap58 bound specifically to HEp-2 and bovine red blood cells. Our findings indicate that the aggregative adherence in the O111:H12 strains may be also mediated by non-fimbrial adhesins. We believe our data contribute to the understanding of the adherence mechanisms of these organisms. 相似文献
749.
Luchetti A Cesari M Carrara G Cavicchi S Passamonti M Scali V Mantovani B 《Journal of molecular evolution》2003,56(5):587-596
Satellite DNA variability follows a pattern of concerted evolution through homogenization of new variants by genomic turnover mechanisms and variant fixation by chromosome redistribution into new combinations with the sexual process. Bacillus taxa share the same Bag320 satellite family and their reproduction ranges from strict bisexuality (B. grandii) to automictic (B. atticus) and apomictic (B. whitei = rossius/ grandii; B. lynceorum = rossius/grandii/atticus) unisexuality. Thelytokous reproduction clearly allows uncoupling of homogenization from fixation. Both trends and absolute values of satellite variability were analyzed in all Bacillus taxa but B. rossius, on 906 sequenced monomers at all level of comparisons: intraspecimen, intrapopulation, interpopulation, intersubspecies, and interspecies. For unisexuals, allozymic and mitochondrial clones were also taken into account. Different reproductive modes (sexual/parthenogenetic) appear to explain observed variability trends, supporting Dover's hypothesis of sexuality acting as a driving force in the fixation of sequence variants, but the present analyses also highlight current spreading of new variants in B. grandii maretimi specimens and point to a biased sequence inheritance at the time of hybrid onset in the apomictic hybrids B. whitei and B. lynceorum. Evidence of biased gene conversion events suggests that, given enough time, sequence homogenization can take place in a unisexual such as B. lynceorum. On the contrary, the absolute values of sequence diversity in each taxon are linked to the species' range, time of divergence, and repeat copy number and, possibly, to transposon features. Satellite dynamics appears therefore to be the outcome of both general molecular processes and specific organismal traits. 相似文献
750.
Cesare Cuspidi Iassen Michev Stefano Meani Cristiana Valerio Giovanni Bertazzoli Fabio Magrini Alberto Zanchetti 《Cardiovascular ultrasound》2003,1(1):1-9