Transposition into replicating DNA occurs through interaction with the processivity factor.

The bacterial transposon Tn7 directs transposition into actively replicating DNA by a mechanism involving the transposon-encoded protein TnsE. Here we show that TnsE physically and functionally interacts with the processivity factor of the DNA replication machinery in vivo and in vitro. Our work establishes an in vitro TnsABC+E transposition reaction reconstituted from purified proteins and target DNA structures. Using the in vitro reaction we confirm that the processivity factor specifically reorders TnsE-mediated transposition events on target DNAs in a way that matches the bias with active DNA replication in vivo. The TnsE interaction with an essential and conserved component of the replication machinery, and a DNA structure reveals a mechanism by which Tn7, and probably other elements, selects target sites associated with DNA replication.

Identification of YidC residues that define interactions with the Sec Apparatus.

In bacteria, a subset of membrane proteins insert into the membrane via the Sec apparatus with the assistance of the widely conserved essential membrane protein insertase YidC. After threading into the SecYEG translocon, transmembrane segments of nascent proteins are thought to exit the translocon via a lateral gate in SecY, where YidC facilitates their transfer into the lipid bilayer. Interactions between YidC and components of the Sec apparatus are critical to its function. The first periplasmic loop of YidC interacts directly with SecF. We sought to identify the regions or residues of YidC that interact with SecY or with additional components of the Sec apparatus other than SecDF. Using a synthetic lethal screen, we identified residues of YidC that, when mutated, led to dependence on SecDF for viability. Each residue identified is highly conserved among YidC homologs; most lie within transmembrane domains. Overexpression of SecY in the presence of two YidC mutants partially rescued viability in the absence of SecDF, suggesting that the corresponding wild-type YidC residues (G355 and M471) participate in interactions, direct or indirect, with SecY. Staphylococcus aureus YidC complemented depletion of YidC, but not of SecDF, in Escherichia coli. G355 of E. coli YidC is invariant in S. aureus YidC, suggesting that this highly conserved glycine serves a conserved function in interactions with SecY. This study demonstrates that transmembrane residues are critical in YidC interactions with the Sec apparatus and provides guidance on YidC residues of interest for future structure-function analyses.

Biogenesis of YidC cytoplasmic membrane substrates is required for positioning of autotransporter IcsA at future poles.

Localization of proteins to specific sites within bacterial cells is often critical to their function. In rod-shaped bacteria, proteins involved in diverse and important cell processes localize to the cell poles. The molecular mechanisms by which these proteins are targeted to the pole, however, are poorly understood. The Shigella autotransporter protein IcsA, which is localized to the pole on the surface of the bacterium, is targeted to the pole in the cytoplasm by a mechanism that is conserved across multiple Gram-negative bacterial species and has thus served as an important and informative model for studying polar localization. We present evidence that in Escherichia coli, the establishment of polar positional information recognized by IcsA requires the activity of the cytoplasmic membrane protein insertase YidC. We show that the role of YidC in IcsA localization is independent of the cell septation and cytokinesis proteins FtsQ and FtsEX. FtsQ is required for polar localization of IcsA and, based on cross-linking studies, is inserted in the vicinity of YidC, but, we find, is not dependent on YidC for membrane insertion. FtsEX is a YidC substrate, but we find that it is not required for polar localization of IcsA. These findings indicate that polar positional information recognized by IcsA depends on one or more membrane proteins that require YidC for proper membrane insertion.

[Relationship between antibiotic resistance and integrons of Escherichia coli isolated from food].

OBJECTIVE: To investigate the relationship between antibiotic resistance of Escherichia coli strains isolated from food and the integrons they harbored. METHODS: PCRs amplifying intI gene and the variable region between the conserved segments (CS-PCR) were performed for class1, class2, and class 3 integron. And the integron content of every isolate was characterized by RFLP analysis and sequencing. RESULTS: 19 of 50 isolates were identified as being positive for integrase 1 gene in the genomic DNA, of which 13 had detectable amplification products for CS-PCR. Two E. coli isolates had class 2 integron. All the integron-positive strains were resistance to at least 4 antibiotics. Most of the gene cassettes integrated in the integrons conferred resistance against trimethoprim and streptomycin-spectinomycin, and the integrons with the dfr17-aadA5 gene cassettes combination were predominant. Some strains with different antibiotic resistance profile or plasmid profile were found to have the same integron. CONCLUSION: There was a good correlation between Integron-carrying and the antibiotic resistance of Escherichia coli strains isolated from food, but in terms of an individual strain, its antibiotic profile was not consistent with the gene cassettes of the integron it harbored.

[Effect of high-oxygen water on enhancing anoxia endurance and anti-fatigue function and the possible mechanism].

OBJECTIVE: To investigate the effect of high-oxygen water on anoxia endurance and anti-fatigue function in mice and explore the possible mechanism. METHODS: KM mice were used. Their body weight, serum urea nitrogen, hepatic glycogen, swimming-sustaining time of mice with a load, plasma lactic acid content, survival time under anoxia or sodium nitrite poisoning were measured. RESULTS: It was found that high-oxygen water can prolong swimming time and can protract the anoxia survival time of mice under normal pressure and being afflicted with acute cerebral ischemia (P<0.05). It can also decrease the level of serum urea nitrogen after exercise (P<0.05) and increase hepatic glycogen storage (P<0.05). CONCLUSION: The results demonstrate that high-oxygen water can enhance the emergent survival ability of mice, the ability of fatigue recovery and anoxia endurance function. It also can increase the energy storage.