Genetic and molecular characterization of essential components of the Vibrio anguillarum plasmid-mediated iron-transport system

The iron-transport genes from the pJM1 plasmid of Vibrio anguillarum have been cloned and sequenced. Five open-reading frames have been identified, one of which encodes the outer membrane receptor for ferric anguibactin, OM2. This coding region corresponds to a protein of 726 amino acids with a Mr of 78,777. The protein has a hydrophobic signal sequence of 35 amino acids and a potential membrane-associated hydrophobic region at the carboxyl terminus. A 2.3-kilobase iron-regulated mRNA was transcribed from this region in vivo. The four other open-reading frames were shown to be involved in the regulation of OM2 expression and in iron transport by the use of insertion mutagenesis and complementation analysis. One of these open-reading frames, ORF3, encodes a 40-kDa polypeptide which, as deduced from the amino acid sequence and the hydropathy plot, is likely to be membrane-associated and together with OM2 may play a role in the transport of iron into the cell cytosol.     

Chloroplast genomes of the diatoms <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis> and <Emphasis Type="Italic">Thalassiosira pseudonana</Emphasis>: comparison with other plastid genomes of the red lineage

The chloroplast genomes of the pennate diatom Phaeodactylum tricornutum and the centric diatom Thalassiosira pseudonana have been completely sequenced and are compared with those of other secondary plastids of the red lineage: the centric diatom Odontella sinensis, the haptophyte Emiliania huxleyi, and the cryptophyte Guillardia theta. All five chromist genomes are compact, with small intergenic regions and no introns. The three diatom genomes are similar in gene content with 127-130 protein-coding genes, and genes for 27 tRNAs, three ribosomal RNAs and two small RNAs (tmRNA and signal recognition particle RNA). All three genomes have open-reading frames corresponding to ORFs148, 355 and 380 of O. sinensis, which have been assigned the names ycf88, ycf89 and ycf90. Gene order is not strictly conserved, but there are a number of conserved gene clusters showing remnants of red algal origin. The acpP, tsf and psb28 genes appear to be on the way from the plastid to the host nucleus, indicating that endosymbiotic gene transfer is a continuing process.     

An unexpected gene cluster for downstream degradation of alkylphenols in Sphingomonas sp. strain TTNP3

In silico analysis of nucleotide sequences flanking the recently found hydroquinone dioxygenase in Sphingomonas sp. strain TTNP3 revealed a gene cluster that encodes a hydroquinone catabolic pathway. In addition to the two open-reading frames encoding the recently characterized hydroquinone dioxygenase, the cluster consisted of six open-reading frames. We were able to express the three open-reading frames, hqdC, hqdD, and hqdE, and demonstrated that the three gene products, HqdC, HqdD, and HqdE had 4-hydroxymuconic semialdehyde dehydrogenase, maleylacetate reductase, and intradiol dioxygenase activity, respectively. Surprisingly, the gene cluster showed similarities to functionally related clusters found in members of the β- and γ-proteobacteria rather than to those found in other members of the genus Sphingomonas sensu latu.     

Isolation and characterisation of components of the <Emphasis Type="Italic">Dunaliella tertiolecta</Emphasis> chloroplast genome

Three chloroplast genes, psbA, psbB and rbcL, of the microalgae Dunaliella tertiolecta were targeted with the view to using these components in the construction of a chloroplast transformation vector. The three genes and surrounding genomic regions were isolated by screening libraries and using degenerate primers to amplify by PCR conserved coding regions and unknown flanking sequences. The putative Dunaliella psbA, psbB and rbcL proteins show high levels of sequence conservation sharing approximately 87, 92 and 97% similarity to the homologues of Chlamydomonas reinhardtii. Interestingly, four of the five introns of the psbA gene contain long open-reading frames which have sequence similarity to the H-N-H and GIY-YIG site-specific homing endonucleases suggesting that, like other microalgae, the Dunaliella gene contains group I introns. Putative promoter regions of the psbB and rbcL genes were isolated and found to contain the required signals necessary for gene expression.     

SRAP技术在遗传的研究进展

SRAP是一种新型的DNA分子标记,具有简便、稳定、中等产率和容易得到选择条带序列的特点。SRAP利用独特的引物设计对开放读码框(ORFs)进行扩增,上游引物长17bp,对外显子进行特异扩增,下游引物长18bp,对内含子区域、启动子区域进行特异扩增,因个体不同及其物种的内含子、启动子与间隔长度不等而产生多态性。本文阐述SRAP的原理和操作流程,综述了SRAP标记目前在植物遗传图谱构建、遗传多样性、基因定位、基因克隆、杂种优势利用等方面的研究进展及应用前景。     

Pcal_1311, an alcohol dehydrogenase homologue from Pyrobaculum calidifontis,displays NADH-dependent high aldehyde reductase activity

Extremophiles - Genome sequence of Pyrobaculum calidifontis, a hyperthermophilic archaeon, harbors three open-reading frames annotated as alcohol dehydrogenases. One of them, Pcal_1311, does not...     

Pentamidine inhibits mitochondrial intron splicing and translation in Saccharomyces cerevisiae

Pentamidine inhibits in vitro splicing of nuclear group I introns from rRNA genes of some pathogenic fungi and is known to inhibit mitochondrial function in yeast. Here we report that pentamidine inhibits the self-splicing of three group I and two group II introns of yeast mitochondria. Comparison of yeast strains with different configurations of mitochondrial introns (12, 5, 4, or 0 introns) revealed that strains with the most introns were the most sensitive to growth inhibition by pentamidine on glycerol medium. Analysis of blots of RNA from yeast strains grown in raffinose medium in the presence or absence of pentamidine revealed that the splicing of seven group I and two group II introns that have intron reading frames was inhibited by the drug to varying extents. Three introns without reading frames were unaffected by the drug in vivo, and two of these were inhibited in vitro, implying that the drug affects splicing by acting directly on RNA in vitro, but on another target in vivo. Because the most sensitive introns in vivo are the ones whose splicing depends on a maturase encoded by the intron reading frames, we tested pentamidine for effects on mitochondrial translation. We found that the drug inhibits mitochondrial but not cytoplasmic translation in cells at concentrations that inhibit mitochondrial intron splicing. Therefore, pentamidine is a potent and specific inhibitor of mitochondrial translation, and this effect explains most or all of its effects on respiratory growth and on in vivo splicing of mitochondrial introns.