Association Between Blood Pressure Lowering and Quality of Life by Treatment of Azilsartan.

The authors assessed the effects of switching from a conventional angiotensin II receptor blocker (ARB) to azilsartan on blood pressure (BP) and health-related quality of life (HR-QOL) in patients with uncontrolled hypertension. Key eligibility criteria were uncontrolled hypertension treated for ≥ 1 month with an ARB, excluding azilsartan, that did not reach the target BP. We recruited 147 patients (64 males and 83 females; mean ± standard deviation age 73 ± 15 years). Azilsartan reduced both systolic and diastolic BP significantly, from 151 ± 16/82 ± 12 to 134 ± 17/73 ± 12 mm Hg, 3 months after switching. Although scores on the comprehensive QOL scale, the EuroQoL 5 dimensions (EQ5D), and the simplified menopausal index (SMI) did not change, the Geriatric Depression Scale (GDS) score improved significantly, and there was a significant association between the change in the GDS score and systolic BP lowering (r = 0.2554, P = 0.030). The Pittsburgh sleep quality index (PSQI) improved significantly only in the female subgroup. Besides sufficient BP lowering activity, anti-hypertensive treatment with azilsartan may have a favorable impact on depression in geriatric patients with uncontrolled hypertension.

Effects of sitagliptin beyond glycemic control: focus on quality of life.

BACKGROUND: Recently, incretin hormones, including glucagon-like peptide-1 (GLP-1) analogue and dipeptidyl peptidase-4 (DPP-4) inhibitor, have been found to regulate glucose metabolism. The aim of this study was to elucidate the efficacy and safety of the clinical usage of DPP-4 inhibitors in Japan. METHODS: This study was designed as a prospective, open-label, multi-center trial. Patients with diabetes mellitus type 2 (T2DM) with poor glycemic profiles (HbA1c ≥ 6.2%) in spite of receiving a medical diet, therapeutic exercise, and/or medications were eligible for this study. The participants received 50 to 100 mg of the DPP-4 inhibitor sitagliptin once daily for 12 months. RESULTS: One hundred and eighty-eight subjects were enrolled. After 12 months of sitagliptin treatment, HbA1c levels decreased (7.65% ± 1.32% to 7.05% ± 1.10%, p < 0.001) as well as fasting plasma glucose (FPG) (145 ± 52 mg/dl to 129 ± 43 mg/dl, p = 0.005). The rate of glycemic control achieved (in accordance with the guidelines of the Japanese Diabetes Society) significantly increased. Blood pressure and serum levels of triglycerides and total cholesterol decreased significantly. Furthermore, the Pittsburgh Sleep Quality Index (PSQI) and Diabetes Symptomatic Scores improved significantly. Adverse events such as hypoglycemia and loss of consciousness occurred in twenty three subjects (11%). CONCLUSIONS: These results suggest that the actions of DPP-4 inhibitors improve not only glycemic control, but also blood pressure, lipid profiles, and quality of life (QOL). Sitagliptin is a sound agent for use in the comprehensive treatment of patients with T2DM.

Controlling pH in shake flasks using polymer-based controlled-release discs with pre-determined release kinetics.

BACKGROUND: There are significant differences in the culture conditions between small-scale screenings and large-scale fermentation processes. Production processes are usually conducted in fed-batch cultivation mode with active pH-monitoring and control. In contrast, screening experiments in shake flasks are usually conducted in batch mode without active pH-control, but with high buffer concentrations to prevent excessive pH-drifts. These differences make it difficult to compare results from screening experiments and laboratory and technical scale cultivations and, thus, complicate rational process development. In particular, the pH-value plays an important role in fermentation processes due to the narrow physiological or optimal pH-range of microorganisms. To reduce the differences between the scales and to establish a pH-control in shake flasks, a newly developed easy to use polymer-based controlled-release system is presented in this paper. This system consists of bio-compatible silicone discs embedding the alkaline reagent Na2CO3. Since the sodium carbonate is gradually released from the discs in pre-determined kinetics, it will ultimately compensate the decrease in pH caused by the biological activity of microorganisms. RESULTS: The controlled-release discs presented here were successfully used to cultivate E. coli K12 and E. coli BL21 pRSET eYFP-IL6 in mineral media with glucose and glycerol as carbon (C) sources, respectively. With glucose as the C-source it was possible to reduce the required buffer concentration in shake flask cultures by 50%. Moreover, with glycerol as the C-source, no buffer was needed at all. CONCLUSIONS: These novel polymer-based controlled-release discs allowed buffer concentrations in shake flask media to be substantially reduced or omitted, while the pH remains in the physiological range of the microorganisms during the whole cultivation time. Therefore, the controlled-release discs allow a better control of the pH, than merely using high buffer concentrations. The conditions applied here, i.e. with significantly reduced buffer concentrations, enhance the comparability of the culture conditions used in screening experiments and large-scale fermentation processes.

Topological transition in dynamic complex networks.

Using a network model involving statistical mechanics we study the topological transition of complex networks with evolving wiring structure. The evolution rule of our network model contains both a structuring effect originated in a wiring decision metric (local clustering coefficient) and a randomizing effect due to thermal fluctuation. Monte Carlo simulation results show a dramatic topological transition between nonclustered networks and clustered networks in response to changes in the degree of randomness.

Efficacy and safety of sitagliptin in elderly patients with type 2 diabetes mellitus.

AIM: The aim of the present study was to assess the efficacy and safety of sitagliptin in elderly patients with type 2 diabetes mellitus. METHODS: A total of 188 patients were enrolled who had type 2 diabetes mellitus with poor glycemic profiles (hemoglobin A1c [HbA1c] ≥6.2%). Patients were assigned to one of three age groups (<65, 65-74 and ≥75 years) and received 50-100 mg of sitagliptin daily for 12 months. Changes in HbA1c classified by age and body mass index (BMI) were assessed in addition to physiological parameters. RESULTS: Mean HbA1c decreased significantly in all age groups (<65 years 8.01 ± 1.59% to 7.29 ± 1.23%; 65-74 years 7.61 ± 1.11% to 7.05 ± 0.99%; ≥75 years 7.21 ± 0.87% to 6.74 ± 0.96%). Reductions in HbA1c were not significantly different among age groups (P = 0.324). In older patients aged 65-74 years and ≥75 years, HbA1c decreased significantly in lean (BMI <25 kg/m2 ) patients (7.52 ± 1.10% to 6.99 ± 1.08%; P < 0.001) and in obese (BMI ≥25 kg/m2 ) patients (7.25% ± 0.90% to 6.86% ± 0.86%; P = 0.015); the changes in HbA1c were not significantly different between the lean and the obese groups (P = 0.943). Adverse events occurred in 12 patients (10.3%) aged ≥65 years, although there was no significant difference among the three age groups. CONCLUSIONS: Sitagliptin treatment offers elderly patients aged ≥65 years efficacious and safe reductions in HbA1c values regardless of BMI. Geriatr Gerontol Int 2018; 18: 631-639.

Roles of the DNA binding proteins H-NS and StpA in homologous recombination and repair of bleomycin-induced damage in Escherichia coli.

The DNA binding protein H-NS promotes homologous recombination in Escherichia coli, but the role of its paralog StpA in this process remains unclear. Here we show that an hns mutant, but not an stpA mutant, are marginally defective in conjugational recombination and is sensitive to the double-strand-break-inducing agent bleomycin. Interestingly, the hns stpA double mutant is severely defective in homologous recombination and more bleomycin-sensitive than is the hns or stpA single mutant, indicating that the stpA mutation synergistically enhances the defects of homologous recombination and the increased bleomycin-sensitivity in the hns mutant. In addition, the transduction analysis in the hns stpA double mutant indicated that the stpA mutation also enhances the defect of recombination in the hns mutant. These results suggest that H-NS plays an important role in both homologous recombination and repair of bleomycin-induced damage, while StpA can substitute the H-NS function. The recombination analysis of hns single, stpA single, and hns stpA double mutants in the recBC sbcA and recBC sbcBC backgrounds suggested that the reduction of the hns single or hns stpA double mutants may not be due to the defect in a particular recombination pathway, but may be due to the defect in a common process of the pathways. The model for the functions of H-NS and StpA in homologous recombination and double-strand break repair is discussed.

Signet ring cell carcinoma of the lower bile duct with rapid growth: report of a case.

Signet ring cell carcinoma occurring in the biliary tract is extremely rare. We herein report the case of a 78-year-old Japanese woman demonstrating signet ring cell carcinoma of the lower bile duct with a rapid growth. Computed tomography of the pancreas head pointed out a circular thickness in the lower bile ductal wall and stenosis of the common bile duct. Cholangiography revealed tapering stenosis at the lower bile duct. Biopsy specimens taken from these lesions and scratched specimens taken from stenotic portion of the lower bile duct were analyzed and demonstrated signet ring cell carcinoma. To the best of our knowledge, this is the first reported case of primary signet ring cell carcinoma of the lower bile duct reported in the English literature. Based on our experience, signet ring cell carcinoma of the lower bile duct is considered to demonstrate both transmural dispersion and an aggressive nature.

Effects of candesartan for middle-aged and elderly women with hypertension and menopausal-like symptoms.

Hypertension in middle-aged or elderly women is often accompanied with various symptoms, which may be related to climacteric. The symptoms of post-menopausal women are suggested to be derived in part from instability of the sympathetic nerve system due to a low estrogen state. An angiotensin-receptor blocker, candesartan cilexetil (candesartan), is known to suppress sympathetic nerve activity by inhibiting the renin-angiotensin system in the brain, suggesting that it may be effective for ameliorating these symptoms. The aim of this study was to elucidate whether candesartan improves menopausal symptoms in hypertensive women. A total of 69 female patients, aged 40 years or older, who had hypertension and various menopausal-like symptoms, were recruited from 39 centers to participate in this study. Patients were prescribed candesartan 4 to 8 mg/day (average dose 7.2 mg/day), alone or in addition to current antihypertensive medications. We interviewed patients in regard to their menopausal symptoms and scored them using the Simplified Menopausal Index (SMI). During the 12-month observation period, significant decreases were seen in both blood pressure (157+/-21/85+/-11 to 141+/-18/77+/-12 mmHg, p<0.001) and SMI (29+/-18 to 18+/-7, p<0.001), although the heart rate did not change. The percentage of decrease in SMI was correlated with that in systolic blood pressure (r=0.43, p<0.001). Candesartan may be an effective antihypertensive agent to relieve menopausal-like symptoms in middle-aged or elderly hypertensive women.

The role of UvrD in RecET-mediated illegitimate recombination in Escherichia coli.

To study the mechanism of RecET-mediated illegitimate recombination, we examined the formation of lambdabio-transducing phage in Escherichia coli in the presence or absence of UV irradiation. We have previously reported that coexpression of RecE and RecT enhances the frequency of recA-independent illegitimate recombination. RecJOR proteins are required for this RecET-mediated illegitimate recombination, and RecQ suppresses it. Here, we showed that the frequencies of both spontaneous and UV-induced RecET-mediated illegitimate recombination events are reduced by a uvrD mutation. It should be noted that UvrD is required for illegitimate recombination only in the presence, but not in the absence, of RecET. In contrast, frequencies of RecET-mediated illegitimate recombination were not affected by ruvAB, ruvC, recG, and recN mutations. The frequency of spontaneous and UV-induced illegitimate recombination in the uvrD recR double mutant was comparable to that of the uvrD single mutant, suggesting that UvrD works at the same step as RecR in the RecET-mediated recombination pathway. Nucleotide sequence analyses of the recombination junctions showed that RecET-mediated illegitimate recombination detected in UvrD-deficient strain is short-homology-dependent. Based on these and previous results, we propose a model for the role of UvrD on RecET-mediated illegitimate recombination.

Yeast recombination pathways triggered by topoisomerase II-mediated DNA breaks.

Topoisomerase II is a ubiquitous enzyme that removes knots and tangles from the genetic material by generating transient double-strand DNA breaks. While the enzyme cannot perform its essential cellular functions without cleaving DNA, this scission activity is inherently dangerous to chromosomal integrity. In fact, etoposide and other clinically important anticancer drugs kill cells by increasing levels of topoisomerase II-mediated DNA breaks. Cells rely heavily on recombination to repair double-strand DNA breaks, but the specific pathways used to repair topoisomerase II-generated DNA damage have not been defined. Therefore, Saccharomyces cerevisiae was used as a model system to delineate the recombination pathways that repair DNA breaks generated by topoisomerase II. Yeast cells that expressed wild-type or a drug-hypersensitive mutant topoisomerase II or overexpressed the wild-type enzyme were examined. Based on cytotoxicity and recombination induced by etoposide in different repair-deficient genetic backgrounds, double-strand DNA breaks generated by topoisomerase II appear to be repaired primarily by the single-strand invasion pathway of homologous recombination. Non-homologous end joining also was triggered by etoposide treatment, but this pathway was considerably less active than single-strand invasion and did not contribute significantly to cell survival in S.cerevisiae.

Characterization and mutational analysis of the RecQ core of the bloom syndrome protein.

Bloom syndrome protein forms an oligomeric ring structure and belongs to a group of DNA helicases showing extensive homology to the Escherichia coli DNA helicase RecQ, a suppressor of illegitimate recombination. After over-production in E.coli, we have purified the RecQ core of BLM consisting of the DEAH, RecQ-Ct and HRDC domains (amino acid residues 642-1290). The BLM(642-1290) fragment could function as a DNA-stimulated ATPase and as a DNA helicase, displaying the same substrate specificity as the full-size protein. Gel-filtration experiments revealed that BLM(642-1290) exists as a monomer both in solution and in its single-stranded DNA-bound form, even in the presence of Mg(2+) and ATPgammaS. Rates of ATP hydrolysis and DNA unwinding by BLM(642-1290) showed a hyperbolic dependence on ATP concentration, excluding a co-operative interaction between ATP-binding sites. Using a lambda Spi(-) assay, we have found that the BLM(642-1290) fragment is able to partially substitute for the RecQ helicase in suppressing illegitimate recombination in E.coli. A deletion of 182 C-terminal amino acid residues of BLM(642-1290), including the HRDC domain, resulted in helicase and single-stranded DNA-binding defects, whereas kinetic parameters for ATP hydrolysis of this mutant were close to the BLM(642-1290) values. This confirms the prediction that the HRDC domain serves as an auxiliary DNA-binding domain. Mutations at several conserved residues within the RecQ-Ct domain of BLM reduced ATPase and helicase activities severely as well as single-stranded DNA-binding of the enzyme. Together, these data define a minimal helicase domain of BLM and demonstrate its ability to act as a suppressor of illegitimate recombination.

Effect of the DNA topoisomerase II inhibitor VP-16 on illegitimate recombination in yeast chromosomes.

Etoposide and teniposide, derivatives of podophyllotoxin, are inhibitors of DNA topoisomerase II and are potent anticancer agents. An adverse effect linked to the use of these drugs is the development of acute myeloid leukemia, a disorder usually associated with chromosomal translocation. To examine podophyllotoxin-induced DNA rearrangement, we developed an assay system to measure illegitimate recombination in Saccharomyces cerevisiae chromosomes. This approach uses juxtaposed CAN1-CYH2 negative selection markers that are introduced into the LEU2 locus, which is located on chromosome III, in a yeast strain carrying the mutated can1 and cyh2 genes. Upon formation of a deletion over the active CAN1-CYH2 genes, a cell becomes resistant to both canavanine and cycloheximide. To introduce drugs into the cell, we used a yeast strain carrying an ISE2 mutation, thereby making the cell drug-permeable. Here we show that treatment of cells with etoposide (VP-16) increases the rate of illegitimate recombination in yeast, indicating that VP-16 stimulates DNA topoisomerase-mediated illegitimate recombination. Structural analysis of the resulting recombinants indicate that most are formed by deletion mutations on chromosome III, which take place between short homologous regions of DNA. We propose a model for illegitimate recombination, in which VP-16 facilitates formation of a cleavable complex between DNA topoisomerase II and DNA, thus promoting DNA double-strand breakage with the resulting DNA ends joined by a non-homologous mechanism.

Relative biological effectiveness of fission neutrons for producing micronuclei in the root-tip cells of onion seedlings after irradiation as dry seeds.

The relative biological effectiveness (RBE) of mixed neutron and gamma-ray radiation emitted at a 252Cf source at the Research Institute for Radiation Biology and Medicine, Hiroshima University, compared with 60Co gamma-ray radiation was determined. The tissue-absorbed dose contribution of the accompanying gamma radiation was about 35.7% to the total tissue-absorbed dose from the 252Cf mixed radiation. The 252Cf mixed radiation and 60Co gamma rays produced approximate linear changes in the frequency of micronuclei induced in root-tip cells of Allium cepa L. onion seedlings after irradiation as dry dormant seeds with varying absorbed doses in onion seeds. Therefore, the RBE for radiation-induced micronuclei was calculated as the ratio of the slopes for the 252Cf mixed radiation and the 60Co gamma rays. The deduced RBE value of 252Cf mixed radiation to 60Co gamma rays to induce micronuclei in dry dormant onion seed cells was about 90.5 +/- 3.6 (+/- 1sigma); the RBE of neutrons from the 252Cf mixed radiation was about 150 +/- 6 (+/- 1sigma). Furthermore, the sensitivity ratio of the induction rate of micronuclei in dry dormant seeds to that in seedlings by neutrons from 252Cf mixed radiation was significantly different from that by 60Co gamma rays. From these results, we concluded that the repair efficiency of DNA damage induced by neutrons may be different from that by gamma rays.

Energy-dependent RBE of neutrons to induce micronuclei in root-tip cells of Allium cepa onion irradiated as dry dormant seeds and seedlings.

The relative biological effectiveness (RBE) of various energy neutrons produced from a Schenkel-type accelerator at the Research Institute for Radiation Biology and Medicine, Hiroshima University (HIRRAC), compared with 60Co gamma-ray radiation was determined. The neutron radiations and gamma-ray radiation produced good linear changes in the frequency of micronuclei induced in the root-tip cells of Allium cepa onion irradiated as dry dormant seeds (seed assay) and seedlings (seedling assay) with varying radiation doses. Therefore the RBE for radiation-induced micronuclei can be calculated as the ratio of the slopes of the fitted linear dose response for the neutron radiations and the 60Co gamma-ray radiation. The RBE values by seed assay and seedling assay decreased to 174 +/- 7, from 216 +/- 9, and to 31.4 +/- 1.0, from 45.3 +/- 1.3 (one standard error), respectively, when neutron energies increased to 1.0 MeV, from 0.2 MeV, in the present study. Furthermore, the ratio of the micronucleus induction rates of seed assay to seedling assay by gamma-ray radiation was much lower than that by neutron radiations.

[Effects of nutrient solution concentration on inorganic and glycyrrhizin contents of Glycyrrhiza glabra Linn].

Licorice, Glycyrrhiza glabra Linn., is one of herbal medicines widely used for various purposes, including as a sweetener and for gastric ulcer treatment. However, environmental destruction due to the harvesting of wild licorice is becoming a serious problem. We cultured licorice in a hydroponic system to examine the relation between the concentration of nutritional solution applied and glycyrrhizin content to determine the optimal nutrient solution concentration for commercial licorice production. Licorice growth and glycyrrhizin content in the root reached the highest values when the plants received nutrient solution approximately equivalent to a quarter unit of Hoagland solution. The results also indicated that the glycyrrhizin content does not correlate with the concentration of nutrient solution applied and/or inorganic contents absorbed, i.e., licorice may absorb large amounts of nutrient solution but the glycyrrhizin content may not increase.

Antihypertensive treatment using an angiotensin receptor blocker and a thiazide diuretic improves patients' quality of life: the Saga Challenge Antihypertensive Study (S-CATS).

The aim of the Saga Challenge Antihypertensive Study (S-CATS), a single-arm, prospective and multi-center trial, was to evaluate the effectiveness of combined antihypertensive treatment with losartan and hydrochlorothiazide (HCTZ). Enrolled in the study were a total of 161 patients with hypertension, who in spite of treatment with an angiotensin receptor blocker (ARB) alone or an ARB and calcium channel blocker (CCB), had not been able to reach blood pressure control goals set by the Japanese Society of Hypertension Guidelines (JSH 2004). The ARBs were replaced with a combination pill containing losartan (50 mg) and HCTZ (12.5 mg), and this treatment was continued for 3 months. This change in therapy resulted in significant decreases in systolic (158±14 to 137±15 mm Hg, P<0.001) and diastolic (85±11 to 76±10 mm Hg, P<0.001) blood pressure and heart rate (73±3 to 72±3) during the study. The patients' quality of life (QOL) score, the EuroQol 5 dimensions (EQ-5D) and the visual analog scale (VAS) (n=96; 70.0 (68.8-80.0) to 80.0 (70.0-90.0), P<0.01) all improved significantly. Another QOL score, the hypertension symptom score (HSS), which we originally developed for the S-CATS trial, decreased significantly (n=93; 4.0 (1.0-9.0) to 2.0 (1.0-8.0), P<0.05). The Pittsburgh sleep quality index (PSQI), which is a psychometric assessment of subjective sleep quality, also decreased significantly (n=45; 4.0 (2.0-7.0) to 3.0 (2.0-5.0), P<0.05). There was a significant correlation between a change in HSS (baseline value -3-months value) and a decrease in systolic blood pressure (n=93; R=0.241, P<0.05). These results suggest that an anti-hypertensive treatment combined with an ARB and a thiazide diuretic may improve patients' QOL, including sleep quality.

Potential benefit of statin therapy for dyslipidemia with chronic kidney disease: Fluvastatin Renal Evaluation Trial (FRET).

BACKGROUND: Dyslipidemia is a common complication of chronic kidney disease (CKD) and contributes to cardiovascular morbidity and mortality of CKD patients. AIM: The aim of the present study was to determine whether fluvastatin, which is mostly characterized by its pleiotropic anti-oxidant effects, has renoprotective effects in dyslipidemic patients with CKD. METHODS: In 43 dyslipidemic patients with CKD taking fluvastatin 10 mg/day, 20 mg/day or 30 mg/day, renal functions as well as lipid profiles were assessed. RESULTS: After 3 months of treatment with fluvastatin, LDL-cholesterol level significantly decreased. Serum creatinine level, estimated glomerular filtration rate (eGFR), urinary albumin excretion (UAE), urinary liver-type fatty acid binding protein (L-FABP) level and urinary 8-hydroxydeoxyguanosine (8-OHdG) level did not change in overall patients. However, in patients with microalbuminuria (baseline UAE ≥ 30 mg/g·creatinine; n = 23), the UAE significantly decreased [2.43 ± 0.67 to 1.98 ± 0.80 log(mg/g·creatinine), p = 0.01]. In patients with high L-FABP group (baseline L-FABP ≥ 11 µg/g·creatinine; n = 18), the urinary L-FABP level was significantly decreased (1.52 ± 0.45 to 1.26 ± 0.43 µg/g·creatinine, p < 0.01). In the limited 23 patients with microalbuminuria, the L-FABP level was significantly decreased [1.20 ± 0.62 to 1.03 ± 0.49 log(µg/g·creatinine), p = 0.042], although the LDL-cholesterol level (139 ± 28 to 129 ± 23 mg/dL, p = 0.08) only showed a tendency to decrease. The 8-OHdG level also was significantly decreased (13.6 ± 9.6 to 9.8 ± 3.8 ng/g·creatinine, p = 0.043). In the overall patients, changes in the values for UAE and urinary L-FABP were not correlated with the changes in LDL-levels. CONCLUSION: Fluvastatin reduces both UAE and the urinary L-FABP level, and thus, has renoprotective effects, independent of its lipid lowering effects in dyslipidemic patients with CKD.

Development of the Handy Bio-Strand and its application to genotyping of OPRM1 (A118G).

We previously developed a three-dimensional microarray system, the Bio-Strand, which exhibits advantages in automated DNA analysis in combination with our Magtration Technology. In the current study, we have developed a compact system for the Bio-Strand, the Handy Bio-Strand, which consists of several tools for the preparation of Bio-Strand Tip, hybridization, and detection. Using the Handy Bio-Strand, we performed single nucleotide polymorphism (SNP) genotyping of OPRM1 (A118G) by allele-specific oligonucleotide competitive hybridization (ASOCH). DNA fragments containing SNP sites were amplified from genomic DNA by PCR and then were fixed on a microporous nylon thread. Thus, prepared Bio-Strand Tip was hybridized with allele-specific Cy5 probes (<15mer), on which the SNP site was designed to be located in the center. By optimizing the amount of competitors, the selectivity of Cy5 probes increased without a drastic signal decrease. OPRM1 (A118G) genotypes of 23 human genomes prepared from whole blood samples were determined by ASOCH using the Handy Bio-Strand. The results were perfectly consistent with those determined by PCR direct sequencing. ASOCH using the Handy Bio-Strand would be a very simple and reliable method for SNP genotyping for small laboratories and hospitals.

Rep helicase suppresses short-homology-dependent illegitimate recombination in Escherichia coli.

To study roles of Rep helicase in short-homology-dependent illegitimate recombination, we examined the effect of a rep mutation on illegitimate recombination and found that the frequency of spontaneous illegitimate recombination is enhanced by the rep mutation. In addition, illegitimate recombination was synergistically enhanced by the rep mutation and UV irradiation, showing that Rep helicase plays a role in suppression of spontaneous as well as UV-induced illegitimate recombination. The defect in RecQ helicase also has a synergistic effect on the increased illegitimate recombination in the rep mutant. It was also found that the illegitimate recombination induced by the rep mutation is independent of the RecA function with or without UV irradiation. Nucleotide sequence analyses of the recombination junctions showed that the illegitimate recombination induced by the rep mutation mostly takes place between short homologous sequences. Based on the fact that the defect of Rep helicase induces replication arrest during replication, resulting in the formation of DNA double-strand breaks, we propose a model for illegitimate recombination, in which double-strand breaks caused by defect of Rep helicase promotes illegitimate recombination via short-homology-dependent-end-joining. In addition, the mechanism of synergistic action between the rep mutation and UV irradiation on illegitimate recombination is discussed.

Illegitimate recombination mediated by double-strand break and end-joining in Escherichia coli.

The frequency of illegitimate recombination has been measured by a lambda bio transducing phage assay during the induction of the E. coli lambda cI857 lysogen. Illegitimate recombination falls into two classes, short homology-independent and short homology-dependent illegitimate recombination. The former involves sequences with virtually no homology, and is mediated by DNA topoisomerases and controlled by the DNA binding protein HU. The latter is induced by UV irradiation or other DNA damaging agents and requires short regions of homology, usually contain 4 to 13 base pairs, at sites involved in recombination. It has been shown that the RecJ exonuclease promotes short homology-dependent illegitimate recombination, but that the RecQ helicase suppresses it. In addition, we have shown that the overexpression of RecE and RecT enhances the frequencies of spontaneous and UV-induced illegitimate recombination and that the RecJ, RecF, RecO, and RecR functions are required for this RecE-mediated illegitimate recombination. Moreover, we have also indicated that RecQ plays a role in the suppression of RecE-mediated illegitimate recombination, with the participation of DnaB, Fis, ExoI, and H-NS. Models have been proposed for these modes of recombination: the DNA gyrase subunit exchange model for short homology-independent illegitimate recombination and the "double-strand break and join" model for short homology-dependent illegitimate recombination. Many features of these models remain to be tested in future studies.