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Circular Molecules (circular + molecule)

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Life Sciences	100%

Selected Abstracts

Isolation and characterization of Tn -Dha1, a transposon containing the tetrachloroethene reductive dehalogenase of Desulfitobacterium hafniense strain TCE1

ENVIRONMENTAL MICROBIOLOGY, Issue 1 2005
Julien Maillard
Summary A new 9.9 kb catabolic transposon, Tn -Dha1, containing the gene responsible for tetrachloroethene (PCE) reductive dechlorination activity, was isolated from Desulfitobacterium hafniense strain TCE1. Two fully identical copies of the insertion sequence ISDha1, a new member of the IS256 family, surround the gene cluster pceABCT, a truncated gene for another transposase and a short open reading frame with homology to a member of the twin-arginine transport system (tatA). Evidence was obtained by Southern blot for an alternative form of the transposon element as a circular molecule containing only one copy of ISDha1. This latter structure most probably represents a dead-end product of the transposition of Tn -Dha1. Strong indications for the transposition activity of ISDha1 were given by polymerase chain reaction (PCR) amplification and sequencing of the intervening sequence located between both inverted repeats (IR) of ISDha1 (IR junction). A stable genomic ISDha1 tandem was excluded by quantitative real-time PCR. Promoter mapping of the pceA gene, encoding the reductive dehalogenase, revealed the presence of a strong promoter partially encoded in the right inverted repeat of ISDha1. A sequence comparison with pce gene clusters from Desulfitobacterium sp. strains PCE-S and Y51 and from Dehalobacter restrictus, all of which show 100% identity for the pceAB genes, indicated that both Desulfitobacterium strains seem to possess the same transposon structure, whereas only the pceABCT gene cluster is conserved in D. restrictus. [source]

Genome characterization, analysis of virulence and transformation of Microbacterium nematophilum, a coryneform pathogen of the nematode Caenorhabditis elegans

FEMS MICROBIOLOGY LETTERS, Issue 2 2006
Tatiana Akimkina
Abstract A coryneform bacterium designated Microbacterium nematophilum has previously been reported to act as a pathogen for Caenorhabditis elegans. This bacterium is able to colonize the rectum of infected worms and cause localized swelling, constipation and slowed growth. Additional isolates and analysis of this bacterium are described here. Tests of pathogenicity on other Caenorhabditis nematodes show that M. nematophilum infection is lethal to most species in the genus, in contrast to its relatively mild effects on C. elegans. The size and geometry of the pathogen genome have been determined as a closed circular molecule of 2.85 Mb with high G+C content. Bacteria also harbor a 55 kb plasmid, pMN1, which is largely composed of a lysogenic bacteriophage genome. Mutagenesis experiments have yielded stable avirulent mutants of M. nematophilum. As a first step towards molecular genetic analysis, methods for low-efficiency transformation of M. nematophilum have been developed. [source]

HPLC purification and re-evaluation of chemical identity of two circular bacteriocins, gassericin A and reutericin 6

LETTERS IN APPLIED MICROBIOLOGY, Issue 4 2010
K. Arakawa
Abstract Aim:, The study aimed for the complete purification and recharacterization of the highly hydrophobic circular bacteriocins, gassericin A and reutericin 6. Methods and Results:, Gassericin A and reutericin 6 were purified to homogeneity using previously described method and reverse-phase HPLC with an octyl column and eluents of aqueous acetonitrile and 2-propanol. Mass analysis, N-terminal sequencing and bacteriocin assay of the HPLC-purified bacteriocins showed the two bacteriocins had identical seamless circular structures with the same m/z value (5651) of [M + H]+ and both had the same specific activity. d/l- amino acid composition analysis using two distinct methods with the chiral fluorescent derivatization reagents (+)-1-(9-fluorenyl)ethyl chloroformate and o -phthalaldehyde/N -acetyl- l -cystein revealed neither gassericin A nor reutericin 6 contained d -alanine residues contrary to our previous results. Conclusion:, Purified gassericin A and reutericin 6 are chemically identical circular molecules containing no d -alanine residues. Significance and Impact of the Study:, The HPLC conditions developed in this study will facilitate advanced purification and correct characterization of other highly hydrophobic bacteriocins. [source]

On the mechanism of loading the PCNA sliding clamp by RFC

MOLECULAR MICROBIOLOGY, Issue 1 2008
Isabelle Dionne
Summary Sliding clamps play central roles in a broad range of DNA replication and repair processes. The clamps form circular molecules that must be opened and resealed around DNA by the clamp loader complex to fulfil their function. While most eukaryotes and many archea possess a homo-trimeric PCNA, the PCNA of Sulfolobus solfataricus is a heterotrimer. Here, we exploit the asymmetry of S. solfataricus PCNA to create a series of circularly permuted PCNA subunit fusions, thereby covalently closing defined interfaces within the heterotrimer. Using these concatamers, we investigate the requirements for loading the clamp onto DNA and reveal that a single defined interface within the heterotrimer is opened during the loading process. Subunit,specific interactions between S. solfataricus RFC clamp loader and PCNA permit us to superimpose our data upon the structure of yeast RFC,PCNA complex, thereby presenting a general model for PCNA loading by RFC in archaea and eukaryotes. [source]

Telomere resolution by Borrelia burgdorferi ResT through the collaborative efforts of tethered DNA binding domains

MOLECULAR MICROBIOLOGY, Issue 3 2007
Yvonne Tourand
Summary Borrelia burgdorferi, a causative agent of Lyme disease, has a highly unusual segmented genome composed of both circular molecules and linear DNA replicons terminated by covalently closed hairpin ends or telomeres. Replication intermediates of the linear molecules are processed into hairpin telomeres via the activity of ResT, a telomere resolvase. We report here the results of limited proteolysis and mass spectroscopy to identify two main structural domains in ResT, separated by a chymotrypsin cleavage site between residues 163 and 164 of the 449 amino acid protein. The two domains have been overexpressed and purified. DNA electrophoretic mobility shift assays revealed that the C-terminal domain (ResT164,449) displays sequence-specific DNA binding to the box 3,4,5 region of the telomere, while the N-terminal domain (ResT1,163) exhibits sequence-independent DNA binding activity. Further analysis by DNase I footprinting supports a model for telomere resolution in which the hairpin binding module of the N-terminal domain is delivered to the box 1,2 region of the telomere through its tethering to ResT164,449. Conversely, ResT1,164 may play an important regulatory role by modulating both sequence-specific DNA binding activity and catalysis by the C-terminal domain. [source]