Economic evaluations of radioembolization with yttrium-90 microspheres in liver metastases of colorectal cancer: a systematic review

BACKGROUND

Transarterial radioembolization with yttrium-90 (Y-90 TARE) microspheres therapy has demonstrated positive clinical benefits for the treatment of liver metastases from colorectal cancer (lmCRC). This study aims to conduct a systematic review of the available economic evaluations of Y-90 TARE for lmCRC.

METHODS

English and Spanish publications were identified from PubMed, Embase, Cochrane, MEDES health technology assessment agencies, and scientific congress databases published up to May 2021. The inclusion criteria considered only economic evaluations; thus, other types of studies were excluded. Purchasing-power-parity exchange rates for the year 2020 ($US PPP) were applied for cost harmonisation.

RESULTS

From 423 records screened, seven economic evaluations (2 cost-analyses [CA] and 5 cost-utility-analyses [CUA]) were included (6 European and 1 USA). All included studies (n = 7) were evaluated from a payer and the social perspective (n = 1). Included studies evaluated patients with unresectable liver-predominant metastases of CRC, refractory to chemotherapy (n = 6), or chemotherapy-naïve (n = 1). Y-90 TARE was compared to best supportive care (BSC) (n = 4), an association of folinic acid, fluorouracil and oxaliplatin (FOLFOX) (n = 1), and hepatic artery infusion (HAI) (n = 2). Y-90 TARE increased life-years gained (LYG) versus BSC (1.12 and 1.35 LYG) and versus HAI (0.37 LYG). Y-90 TARE increased the quality-adjusted-life-year (QALY) versus BSC (0.81 and 0.83 QALY) and versus HAI (0.35 QALY). When considering a lifetime horizon, Y-90 TARE reported incremental cost compared to BSC (range 19,225 to 25,320 $US PPP) and versus HAI (14,307 $US PPP). Y-90 TARE reported incremental cost-utility ratios (ICURs) between 23,875 $US PPP/QALY to 31,185 $US PPP/QALY. The probability of Y-90 TARE being cost-effective at £ 30,000/QALY threshold was between 56% and 57%.

CONCLUSIONS

Our review highlights that Y-90 TARE could be a cost-effective therapy either as a monotherapy or when combined with systemic therapy for treating ImCRC. However, despite the current clinical evidence on Y-90 TARE in the treatment of ImCRC, the global economic evaluation reported for Y-90 TARE in ImCRC is limited (n = 7), therefore, we recommend future economic evaluations on Y-90 TARE versus alternative options in treating ImCRC from the societal perspective.

Economic evaluations of radioembolization with Itrium-90 microspheres in hepatocellular carcinoma: a systematic review

Background

Transarterial radioembolization (TARE) with yttrium-90 microspheres is a clinically effective therapy for hepatocellular carcinoma (HCC) treatment. This study aimed to perform a systematic review of the available economic evaluations of TARE for the treatment of HCC.

Methods

The Preferred Reported Items for Systematic reviews and Meta-Analyses guidelines was followed by applying a search strategy across six databases. All studies identified as economic evaluations with TARE for HCC treatment in English or Spanish language were considered. Costs were adjusted using the 2020 US dollars based on purchasing-power-parity ($US PPP).

Results

Among 423 records screened, 20 studies (6 cost-analyses, 3 budget-impact-analyses, 2 cost-effectiveness-analyses, 8 cost-utility-analyses, and 1 cost-minimization analysis) met the pre-defined criteria for inclusion. Thirteen studies were published from the European perspective, six from the United States, and one from the Canadian perspectives. The assessed populations included early- (n = 4), and intermediate-advanced-stages patients (n = 15). Included studies were evaluated from a payer perspective (n = 20) and included both payer and social perspective (n = 2). TARE was compared with transarterial chemoembolization (TACE) in nine studies or sorafenib (n = 11). The life-years gained (LYG) differed by comparator: TARE versus TACE (range: 1.3 to 3.1), and TARE versus sorafenib (range: 1.1 to 2.53). Of the 20 studies, TARE was associated with lower treatment costs in ten studies. The cost of TARE treatment varied widely according to Barcelona Clinic Liver Cancer (BCLC) staging system and ranged from 1311 $US PPP/month (BCLC-A) to 71,890 $US PPP/5-years time horizon (BCLC-C). The incremental cost-utility ratio for TARE versus TACE resulted in a 17,397 $US PPP/Quality-adjusted-Life-Years (QALY), and for TARE versus sorafenib ranged from dominant (more effectiveness and lower cost) to 3363 $US PPP/QALY.

Conclusions

Economic evaluations of TARE for HCC treatment are heterogeneous. Overall, TARE is a cost-effective short- and long-term therapy for the treatment of intermediate-advanced HCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12876-022-02396-6.

Modulation of the propagation speed of mechanical waves in silicon quantum dots embedded in a silicon-nitride film

Using a vectorial picosecond self-diffraction method, we evaluate the modification of the speed of the sound in a silicon-nitride film containing silicon quantum dots prepared by remote plasma-enhanced chemical vapor deposition. Our non-contact technique is based on the stimulation of the electrostriction contribution to the nonlinearity of index exhibited by the sample in a multiwave mixing laser experiment. We identified the electronic birefringence using two of the incident beams to generate a self-diffraction signal, then, we modified the third order nonlinear response by means of the optical Kerr effect given by a phase-mismatched third beam which induced electrostriction. Our results indicated that the speed of the sound in a silicon-nitride film can be simultaneously tailored by an electronic nonlinear refractive index, and by an electrostriction effect, both resulting from silicon quantum dots doping.

Side effects of rodent control on non-target species: Rodenticides increase parasite and pathogen burden in great bustards

For many years anticoagulant rodenticides have been used in vole control campaigns, in spite of the proven risk of secondary poisoning of non-target predators and scavengers. In this paper we analyse for the first time great bustard exposure and intoxication by anticoagulant rodenticides in Spain, based on residues found in the livers of 71 bustard carcasses collected during 1991-2010. Ten individuals contained chlorophacinone and one flocoumafen. Chlorophacinone level was significantly correlated with the pathogen and parasite burden of intoxicated birds. Moreover, through the last 12 years the annual number of great bustards that present chlorophacinone in liver collected in our study areas was correlated with vole peaks at a nearby area, suggesting that the ingestion of rodenticide was proportional to the amounts spread in the fields. We conclude that rodenticide consumption is a regular event among great bustards when baited cereal is spread on fields, and that this may cause chronic weakening of intoxicated individuals, possibly affecting their survival. Future rodent control actions should consider these negative side effects on non target granivorous steppe and farmland species, particularly when they are globally threatened.

Life-history characteristics of the large Amazonian migratory catfish Brachyplatystoma rousseauxii in the Iquitos region, Peru

The main life-history traits of the dorado Brachyplatystoma rousseauxii, a large Amazonian catfish undertaking the largest migration known for a freshwater fish species (from the nursery area in the estuary of the Amazon to the breeding zones in the head waters of the western Amazon basin close to the Andes), were determined from a 5 year sampling of >15,000 specimens in the Peruvian Amazon. The breeding season occurred during the falling and low-water periods, which is hypothesized to be an adaptation to maximize the chances of young stages to reach the estuary. The size at first sexual maturity was slightly larger for females than males, c. 91 and 83 cm standard length (L(S)), respectively. Both males and females reproduce for the first time at >3 years old. The fecundity per spawning event ranged from 481,734 to 1,045,284 oocytes for females weighing 25 and 34 kg, respectively. Seasonal variations of body condition were similar among sexes, but differed between immature specimens that had a higher condition during the low-water period and lower condition during rising waters, and mature individuals that showed the opposite pattern. The growth characteristics were estimated by L(S) frequency analysis. For females, the best fitting models gave a mean birth date in August, during the height of the breeding cycle, with the following von Bertalanffy growth function parameters: L(Sinfinity) = 153.3, K = 0.29 and t(0) =- 0.37 years. For males, the best fitting model gave a mean birth date in July, also during the height of the breeding period, with L(Sinfinity) = 142, K = 0.30 and t(0) =- 0.36 years. At a given age, females were systematically larger than males and the size difference increased with age. The largest females sampled (148 cm L(S)) was 11 years old and the largest male (134 cm L(S)) was 9 years old. The mortality estimates were higher for males total (Z) = 1.34, natural (M) = 0.52 and fishing (F) = 0.82 than for females (Z = 0.98, M = 0.50, F = 0.48). The life-history patterns of B. rousseauxii are discussed in light of the available knowledge about this species and the understanding of its complex life cycle.

Polymorphous silicon thin films obtained by plasma-enhanced chemical vapor deposition using dichlorosilane as silicon precursor

Polymorphous silicon thin films (pm-Si) have been deposited from mixtures of dichlorosilane and hydrogen, using argon as the diluting gas by plasma-enhanced chemical vapor deposition. The deposition conditions were chosen to simultaneously obtain both Si nanocrystallites and an amorphous silicon matrix in the as-grown samples. High resolution transmission electron microscopy studies show the crystallinity of Si domains whose dimensions are in the interval of 2-14 nm. The surface passivation state of the silicon nanocrystals was inferred from Fourier transform infrared spectroscopy analysis. Two optical absorption edges, corresponding to the amorphous matrix and the Si nanocrystals, were observed for all the pm-Si thin films. Intense visible photoluminescence was observed for the as-grown samples. The possibility of using these thin films for the down-conversion effect in silicon solar cells is discussed.

Modification of the nonlinear optical absorption and optical Kerr response exhibited by nc-Si embedded in a silicon-nitride film

We studied the absorptive and refractive nonlinearities at 532 nm and 26 ps pulses for silicon-nitride films containing silicon nanoclusters (nc-Si) prepared by remote plasma-enhanced chemical vapor deposition (RPECVD). Using a self-diffraction technique, we measured for the as-grown sample beta=7.7x10(-9)m/W, n(2)=1.8x10(-16)m(2)/W, and /chi(3)1111/ = 4.6x10(-10)esu; meanwhile, when the sample was exposed to an annealing process at 1000 degrees C during one hour in a nitrogen atmosphere, we obtained beta=-5x10(-10)m/W, n2=9x10(-17)m(2)/W, and /chi(3)1111/=1.1x10(-10)esu. A pure electronic nonlinear refraction was identified and a large threshold ablation of 41 J/cm(-2) was found for our films. By fitting nonlinear optical transmittance measurements, we were able to estimate that the annealed sample exhibits a response time close to 1 fs. We report an enhancement in the photoluminescence (PL) signal after the annealing process, as well as a red-shift due to an increment in size of the nc-Si during the thermal process.

Photoluminescence of as-grown silicon nanocrystals embedded in silicon nitride: influence of atomic hydrogen abundance

Silicon nanocrystals embedded in silicon nitride films were grown by direct plasma enhanced chemical vapor deposition at 300 degrees C, using mixtures of SiH2Cl2/NH3/H2/Ar. The films composition and chemical stability was tested by Fourier Transform Infrared Spectroscopy and Rutherford Backscattering Spectroscopy. The influence of hydrogen abundance during the deposition process on the photoluminescence of as-grown samples was studied as a function of the radiofrequency power and hydrogen dilution flow rate. In situ Optical Emission Spectroscopy allowed the diagnostic of the species in the plasma region and their general trends as a function of the radiofrequency power. The changes in the hydrogen content and silicon incorporation to the film as a function of the radiofrequency power were discussed in terms of silicon nanocrystals formation and growth in the silicon nitride matrix. The photoluminescence emission from the as-grown samples was found to red-shift with increasing hydrogen abundance. This observation is consistent with the increase in silicon content associated to nc-Si of larger size. On the other hand, the photoluminescence intensity was observed to decrease for very high radiofrequency powers and hydrogen dilutions. High Resolution Transmission Electron Microscopy confirmed the presence of silicon nanocrystals embedded in the amorphous silicon nitride matrix and allowed the correlation between the nanocrystals size and the photoluminescence emission energy using the quantum confinement model.

Thermo-optic effect and optical third order nonlinearity in nc-Si embedded in a silicon-nitride film

Using a self-diffraction experiment with 7ns pulses at 532nm we studied a silicon nitride film containing silicon nanoclusters (nc-Si) of 3.1+/-0.37 nm mean size. The sample was prepared by remote plasma-enhanced chemical vapor deposition (RPECVD), and we found that its nonlinearity consists of a combination of electronic and thermal contributions. By varying the repetition rate of the laser, we discriminated the responsible mechanisms for the nonlinear response. Using this procedure we determined a total /chi((3))1111/ = 3.3x10(-10)esu, n2 = 2.7x10(-16) m(2)/W, beta = 1x10(-9) m/W and dn/dT =1x10(-4) degrees C(-1) for our sample. We also show results for the optical Kerr effect using 80 fs pulses at 820 nm. The purely electronic nonlinearity measured is characterized by /chi((3))1111/=9.5 x10(-11) esu.

[Meta-analysis of the diagnostic performance of 18F-FDG PET in renal cell carcinoma]

AIM

Renal cell carcinoma is the most frequent solid kidney tumor. At present, PET is not the imaging test of choice, the helical CT being the best method to assess these patients. The aim of the study was to perform a meta-analysis of the literature to evaluate the performance and accuracy of 18F-FDG PET in the detection of primary disease, recurrence and metastasis of renal cell carcinoma.

MATERIALS AND METHODS

A systematic search was done of the available literature in primary and secondary databases published until October 2004 indexed in MEDLINE and CANCERLIT. Exclusion/inclusion criteria were applied. Their quality was evaluated using the Flynn criteria and joint estimators of sensitivity (S), specificity (Sp), likelihood ratios (LR), diagnostic odds ratio (DOR) and summary ROC (SROC) curve were obtained. The presence of the threshold effect was evaluated and the summary ROC (SROC) curve was calculated.

RESULTS

Seven out of 46 studies fulfilled the inclusion criteria and were analyzed. Three studies evaluated the use of 18F-FDG PET in the differential diagnosis of renal masses. Two studies analyzed restaging and two analyzed the role of 18F-FDG PET in the detection of metastatic disease. All the selected studies were classified according to Flynn's criteria. We found the highest S in restaging with S 0.87 (95 % CI, 0.75-0.95) and in metastases detection with S 0.72 (95 % CI, 0.56-0.85) as well as the high Sp in differential diagnosis of renal masses.

CONCLUSIONS

The results of this meta-analysis suggest that 18F-FDG PET can be useful in restaging and detection of metastatic disease, based on its acceptable S and Sp. However, the performance of 18F-FDG PET in the detection of primary disease is limited, but this may improve with the new PET/CT systems.

Growth of silicon nanoclusters on different substrates by plasma enhanced chemical vapor deposition

We report an atomic force microscopy study of the early stages of growth of silicon nanoclusters formed on different substrates by plasma-enhanced chemical vapor deposition, using dichlorosilane (SiH2CI2) and hydrogen (H2) as reactive gases. (100) n-type single crystalline silicon, fused silica, amorphous silicon nitride and corning glass, were used as substrates for the growth of the nanoclusters, which were formed at low substrate temperature (200 degrees C). The diameter, height and number density of the clusters were controlled by the deposition time and pressure. It was found that not only the plasma conditions but also the surface characteristics of the substrate influence the cluster density, shape, and size. For the ordered silicon surface and the amorphous fused silica, the nanoclusters result oval in shape and exhibit preferential growth along the surface. When deposited over amorphous silicon nitride and corning glass, the density of nanoclusters increases and there is a tendency toward columnar growth since the diameter of the nanoclusters tends to decrease. We conclude that although the specific features of the nanoclusters originate from the chlorine chemistry introduced by the SiHxCly deposition precursor and the chemical stability of chlorine-terminated surfaces under hydrogen plasma, the surface quality and roughness also plays an important role on the nucleation and mobility of the species. The combination of both effects gives rise to the different nanostructured growths observed.

Diagnosis of orthopedic infection in clinical practice using Tc-99m sulesomab (antigranulocyte monoclonal antibody fragment Fab'2)

OBJECTIVE

The aim of the study was to analyze the use of Tc-99m-labeled antigranulocyte monoclonal antibody fragment Fab'2 (SMab, Leukoscan) in the diagnosis of acute osteomyelitis and articular prosthesis infection. One hundred seventeen patients (118 studies) have been included, 92 women and 25 men. Thirty-seven had a suspicion of osteomyelitis and 81 with suspicion of infection of a hip (35 patients) or a knee (45 patients) prosthesis. The mean age was 64 years. A 3-phase bone scan and a SMab scan were obtained in all patients. Antigranulocyte scans were obtained within 3 and 8 hours postinjection of 20 mCi (740 MBq) of Tc-99m-labeled antibody. Diagnosis of infection was based on bone biopsy in 8 cases and on at least 2 positive cultures in the remaining cases. Infection was ruled out with negative cultures or 1-year patient follow up with negative C-reactive protein and normal erythrocyte sedimentation rate.

RESULTS

Sensitivity, specificity, accuracy, and negative predictive value of Tc 99m-SMab scintigraphy were: 75%, 95%, 87%, and 92% for long bone osteomyelitis and 80%, 89%, 87%, and 91% for articular prosthesis infection, respectively. Positive predictive values were 83% and 63%, respectively.

CONCLUSION

Tc-99m-antigranulocyte monoclonal antibody fragment Fab'2 scintigraphy seems to be a useful method in the diagnosis of osteoarticular infection.

[Graft viability of patients with renal transplantation from non heart beating donors]

INTRODUCTION

Renal transplantation (RT) is currently the treatment of choice in end-stage renal disease. The Gregorio Marañón hospital performed 65 RT, 97.01 pmp, this year.

OBJECTIVE

To study the characteristics which RT patients from non-heart beating donors have in the immediate post-transplantation renogram. To know the evolution of the renal function, by renogram.

METHODS

Ten patients with NHBD graft out of 65 patients with RT were studied in the year 2003.

RESULTS

The study is made up of 10 patients with RT from NHBD, with an average timing of warm ischemia of 35 min and average timing of cool ischemia 21 h. In the post-transplantation renal function study, 9 of then showed hemodilution and one an acute tubular necrosis (ATN) pattern. In most of the cases, the study was performed the day after the RT except for one that was performed on the 4th day (1.7 +/- 1 days). Renal perfusion was conserved in every case. The renal graft maintained this type of record until post-RT day 7 (6.67 +/- 0.57 days) and evolved towards ATN after day 10 (11.65 +/- 1.5 days) and normal range on day 55 +/- 51.1 post-transplantation. All patients supported the graft, with acceptable renal function, except one of then who was treated with transplantectomy due to a renal venous thrombosis.

CONCLUSION

The renal function study showed "hemodilution" in the first post-transplantation in 90 % of the RT from NHBD. Evolution went from ATN to normality. The NHBD are adequate for transplantation, significantly shortening the waiting time for RN.

Crystallization of the Bacillus subtilis SPP1 bacteriophage helicase loader protein G39P

The essential helicase loader protein G39P encoded by Bacillus subtilis SPP1 phage has been overproduced in Escherichia coli and purified. The wild-type protein has been crystallized by the hanging-drop vapour-diffusion method in a primitive hexagonal space group, probably P6(1)22/P6(5)22, but the crystals diffract to only 3.4 A and are poorly reproducible. Mass-spectrometric analysis has revealed marked proteolytic cleavage from the C-terminus and the presence of a major species corresponding to deletion of the 14 C-terminal residues. Thus, a new variant of the protein (G39P112) has been engineered that corresponds to a 14-residue C-terminal truncation. The G39P112 variant has also been crystallized but now in a primitive orthorhombic form, probably P2(1)2(1)2 or P2(1)2(1)2(1), with unit-cell parameters a = 85.6, b = 89.7, c = 47.6 A, with diffraction to 2.4 A on a synchrotron source and with greatly improved reproducibility. Calculation of V(M) values for this G39P112 variant suggests the presence of three monomers in the asymmetric unit, corresponding to a solvent content of about 47%. A selenomethionine-incorporated form of the protein has been produced and a full three-wavelength MAD data collection undertaken.

Effect of the recU suppressors sms and subA on DNA repair and homologous recombination in Bacillus subtilis

In Bacillus subtilis, mutant alleles of the genes sms and subA partially suppress the recombination phenotype of recU cells. When present in an otherwise Rec(+) strain, Delta sms and Delta subA alleles render cells slightly sensitive to DNA-damaging agents, and impair chromosomal transformation (3- to 10-fold reduction), but do not affect plasmid transformation (less than 1.5-fold reduction). The Delta sms and Delta subA alleles were introduced into rec-deficient strains representative of the epistatic groups alpha (recF strain), beta (addA addB), gamma (recH), epsilon (recB, Delta recU and recD strains) and zeta (Delta recS). Both the Delta sms and Delta subA mutations were found to increase sensitivity to DNA-damaging agents in recF, Delta recS and addAB cells. In contrast, the Delta sms mutations decreased the sensitivity of recB, Delta recU, recD and recH cells, and the Delta subA mutation decreased the sensitivity of recB and Delta recU cells to DNA-damaging agents. Functions classified within the epistatic groups alpha, epsilon and zeta are required for intramolecular recombination, measured as plasmid transformation. The Delta sms and Delta subA mutations, which partially suppressed the recombinational repair phenotype of mutants for functions within epistatic group epsilon, enhanced plasmid transformation of recU (recB, recD) and recS cells by 10- to 20-fold. In the absence of the proteins Sms and SubA, the recombination machinery is apparently redirected towards (an) alternative pathway(s). Furthermore, the shared ability of the Delta sms and Delta subA mutations to act as indirect suppressors of recB, recU and recD mutations supports the classification of the recBUD genes within epistatic group epsilon.

Flavones inhibit the hexameric replicative helicase RepA

Helicases couple the hydrolysis of nucleoside triphosphates (NTPs) to the unwinding of double-stranded nucleic acids and are essential in DNA metabolism. Thus far, no inhibitors are known for helicases except heliquinomycin isolated from Streptomyces sp. As the three-dimensional structure of the hexameric replicative DNA helicase RepA encoded by the broad host-range plasmid RSF1010 is known, this protein served as a model helicase to search for inhibitory compounds. The commercially available flavone derivatives luteolin, morin, myricetin and dimyricetin (an oxidation product of myricetin) inhibited the ATPase and double-stranded DNA unwinding activities of RepA. Dimyricetin was the most effective inhibitor for both activities. Single-stranded DNA-dependent RepA ATPase activity is inhibited non-competitively by all four compounds. This finding contrasts the inhibition of phosphoinositide 3-kinase by flavones that fit into the ATP binding pocket of this enzyme. Myricetin also inhibited the growth of a Gram-positive and a Gram-negative bacterial species. As we found other hexameric and non-hexameric prokaryotic helicases to be differentially sensitive to myricetin, flavones may provide substructures for the design of molecules helpful for unraveling the mechanism of helicase action and of novel pharmacologically useful molecules.

Crystal structure of omega transcriptional repressor encoded by Streptococcus pyogenes plasmid pSM19035 at 1.5 A resolution

The 71 amino acid residue omega protein encoded by the Streptococcus pyogenes non-conjugative plasmid pSM19035 is a transcriptional repressor that regulates expression of genes for copy number control and stable maintenance of plasmids. The crystal structure of omega protein has been determined by multiple isomorphous replacement, including anomalous scattering and refined to an R-factor of 21.1 % (R(free)=23.2 %) at 1.5 A resolution. Two monomers related by a non-crystallographic 2-fold axis form a homodimer that occupies the asymmetric unit. Each polypeptide chain is folded into two alpha-helices and one beta-strand forming an antiparallel beta-ribbon in the homodimer. The N-terminal regions (1-23 and 1-22 in subunits I and II, respectively) are not defined in the electron density due to proteolysis of the N-terminal 20 amino acid residues during crystallisation and partial disorder. The omega protein belongs to the structural superfamily of MetJ/Arc repressors featuring a ribbon-helix-helix DNA-binding motif with the beta-ribbon located in and recognizing the major groove of operator DNA; according to a modelled omega protein-DNA complex, residues Arg31 and Arg31' on the beta-ribbon are in positions to interact with a nucleobase, especially guanine.

Genetic recombination in Bacillus subtilis 168: effect of DeltahelD on DNA repair and homologous recombination

The B. subtilis DeltahelD allele rendered cells proficient in transformational recombination and moderately sensitive to methyl methanesulfonate when present in an otherwise Rec(+) strain. The DeltahelD allele was introduced into rec-deficient strains representative of the alpha (recF strain), beta (addA addB), gamma (recH), epsilon (DeltarecU), and zeta (DeltarecS) epistatic groups. The DeltahelD mutation increased the sensitivity to DNA-damaging agents of addAB, DeltarecU, and DeltarecS cells, did not affect the survival of recH cells, and decreased the sensitivity of recF cells. DeltahelD also partially suppressed the DNA repair phenotype of other mutations classified within the alpha epistatic group, namely the recL, DeltarecO, and recR mutations. The DeltahelD allele marginally reduced plasmid transformation (three- to sevenfold) of mutations classified within the alpha, beta, and gamma epistatic groups. Altogether, these data indicate that the loss of helicase IV might stabilize recombination repair intermediates formed in the absence of recFLOR and render recFLOR, addAB, and recH cells impaired in plasmid transformation.

Stability and DNA-binding properties of the omega regulator protein from the broad-host range Streptococcus pyogenes plasmid pSM19035

At the transcriptional level, the pSM19035-encoded omega protein coordinates the expression of proteins required for control of copy number and maintenance of plasmids. Using circular dichroism, fluorescence spectroscopy, ultracentrifugation and an electrophoretic mobility shift assay, the wild-type omega protein and a variant with a C-terminal hexa-histidine tag (omega-H(6)) were characterized. The omega protein is mainly alpha-helical (42%), occurs as homodimer in solution, unfolds thermally with half transition temperatures, T(m), between approximately 43 and approximately 78 degrees C depending on the ionic strength of the buffer, and binds PcopS-DNA with high affinity. The omega-H(6) protein has a modified conformation with lower alpha-helix content (29%), lower thermal stability, and strongly reduced affinity to PcopS-DNA.

Glu-256 is a main structural determinant for oligomerisation of human arginase I

One determinant that could play a role in the quaternary structure of human arginase is the pair of salt links between the strictly conserved residues R255 from one monomer and E256 from every adjacent subunit. In this work, the ionic interaction between monomers was disrupted by expressing a human arginase where Glu-256 had been substituted by Gln. Biochemical analyses of the mutant protein showed that: (i) it shares the wild-type kinetic parameters of the arginine substrate; (ii) E256Q arginase behaves as a monomer by gel filtration; (iii) it is drastically inactivated by dialysis in the presence of EDTA, an inhibitory effect which is reversed by addition of Mn(2+); and (iv) the mutant enzyme loses thermal stability. The lack of oligomerisation for E256Q arginase and the conservation of E256 throughout evolution of the protein family suggest that this residue is involved in the quaternary structure of arginases.

Lithium inhibits caspase 3 activation and dephosphorylation of PKB and GSK3 induced by K+ deprivation in cerebellar granule cells

Lithium protects cerebellar granule cells from apoptosis induced by low potassium, and also from other apoptotic stimuli. However, the precise mechanism by which this occurs is not understood. When cerebellar granule cells were switched to low potassium medium, the activation of caspase 3 was detected within 6 h, suggesting a role of caspase 3 in mediating apoptosis under conditions of low potassium. In the same conditions, lithium (5 mM) inhibited the activation of caspase 3 induced by low potassium. As lithium did not inhibit caspase 3 activity in vitro, these results suggest that this ion inhibits an upstream component that is required for caspase 3 activation. Lithium is known to inhibit a kinase termed glycogen sythase kinase 3 (GSK3), which is implicated in the survival pathway of phosphatidylinositol 3-kinase/protein kinase B (PI3K/PKB). Here we demonstrate that low potassium in the absence of lithium induces the dephosphorylation, and therefore the activation, of GSK3. However, when lithium was present, GSK3 remained phosphorylated at the same level as observed under conditions of high potassium. Low potassium induced the dephosphorylation and inactivation of PKB, whereas when lithium was present PKB was not dephosphorylated. Our results allow us to propose a new hypothesis about the action mechanism of lithium, this ion could inhibit a serine-threonine phosphatase induced by potassium deprivation.

New insights into host factor requirements for prokaryotic beta-recombinase-mediated reactions in mammalian cells

The prokaryotic beta-recombinase catalyzes site-specific recombination between two directly oriented minimal six sites in mammalian cells, both on episomic and chromatin-integrated substrates. Using a specific recombination activated gene expression system, we report the site-specific recombination activity of an enhanced green fluorescent protein (EGFP) fused version of beta-recombinase (beta-EGFP). This allows expression of active beta-recombinase detectable in vivo and in fixed cells by fluorescence microscopy. In addition, cellular viability is compatible with a substantial level of expression of the beta-EGFP protein. Using fluorescence-activated cell sorting, we have been able to enrich cell populations expressing this fusion protein. Application of this strategy has allowed us to study in more depth the host factor requirements for this system. Previous work showed that eukaryotic HMG1 protein was necessary and sufficient to help beta-recombinase activity in vitro. The influence of ectopic expression of HMG1 protein in the recombination process has been analyzed, indicating that HMG1 overexpression does not lead to a significant increase on the efficiency of beta-recombinase-mediated recombination both on episomal substrates and chromatin-associated targets. In addition, beta-recombinase-mediated recombination has been demonstrated in HMG1 deficient cells at the same levels as in wild type cells. These data demonstrate the existence of cellular factors different from HMG-1 that can act as helpers for beta-recombinase activity in the eukaryotic environment.

Crystallization and preliminary X-ray diffraction studies of the epsilonzeta addiction system encoded by Streptococcus pyogenes plasmid pSM19035

The proteins encoded by the Streptococcus pyogenes broad-host range and low copy-number plasmid pSM19035 form a toxin-antitoxin module that secures stable maintenance by causing the death of plasmid-free segregants. The epsilonzeta protein complex was crystallized in four different forms at pH 5.0 and pH 7.0 using the vapour-diffusion method with PEG 3350 and ethylene glycol as precipitants. Three of the crystal forms were obtained in the same droplet under identical conditions at pH 5.0. One form belongs to the enantiomorphic space groups P4(3)2(1)2 or P4(1)2(1)2. For the other two, the X-ray reflection conditions match those of space group P2(1)2(1)2(1), one representing a superlattice of the other. A crystal form growing at pH 7.0 also belongs to space group P2(1)2(1)2(1), but there is no indication of a structural relationship to the other orthorhombic forms. Initially, the crystals diffracted to 2.9 A resolution and diffracted to 1.95 A after soaking at pH 7.0. A preparation of selenomethionyl epsilonzeta protein complex yielded single crystals suitable for X-ray diffraction experiments using synchrotron sources.

[Utility of SPECT with 99m Tc-tetrofosmin and stimulus with dipyridamole in patients with permanent ventricular pacemakers]

BACKGROUND AND OBJECTIVE

Patients with permanent ventricular pacemakers (PP) are a difficult subgroup to assess in the study of coronary artery disease. The objective of this study was to evaluate the diagnostic value of the myocardial perfusion scintigraphy with 99mTC-Tetrofosmin (Tc-Tf) and stimulus with dipyridamole in patients with PP and suspected coronary artery disease.

PATIENTS AND METHODS

Fourteen patients with suspected coronary artery disease and without structural cardiopathy, who underwent Tc-Tf and cardiac catheterization, were studied retrospectively. Sensitivity, specificity, predictive values and Kappa index were calculated for the diagnosis of coronary artery disease, multivessel disease, and for each one of the coronary arteries (left anterior descending, right coronary, and circumflex). In addition, the correlation between the number of territories with perfusion defects and the number of diseased vessels was studied.

RESULTS

In regards to the diagnosis of coronary artery disease, sensitivity, specificity, positive predictive value, negative predictive value and the Kappa index were 100%, 50%, 83%, 100% and 0.55, respectively. For multi-vessel disease, these values were 83%, 64%, 64%, 83% and 0.43 respectively. The correlation coefficient between the number of territories with perfusion defects and the number of diseased vessels was 0.61 (p = 0.02). In the diagnosis of anterior descending disease, sensitivity and specificity were 83% and 88% respectively. For the right coronary artery, these values were 100% and 44% and for the circumflex artery 38% and 83%, respectively.

CONCLUSION

In patients with PP and suspected coronary artery disease, myocardial perfusion scintigraphy with Tc-Tf and stimulus with dipyridamole is of great value in the diagnosis of coronary artery disease and in the assessment of its extension.

Functional analysis of the terminase large subunit, G2P, of Bacillus subtilis bacteriophage SPP1

The terminase of bacteriophage SPP1, constituted by a large (G2P) and a small (G1P) subunit, is essential for the initiation of DNA packaging. A hexa-histidine G2P (H6-G2P), which is functional in vivo, possesses endonuclease, ATPase, and double-stranded DNA binding activities. H6-G2P introduces a cut with preference at the 5'-RCGG downward arrowCW-3' sequence. Distamycin A, which is a minor groove binder that mimics the architectural structure generated by G1P at pac, enhances the specific cut at both bona fide 5'-CTATTGCGG downward arrowC-3' sequences within pacC of SPP1 and SF6 phages. H6-G2P hydrolyzes rATP or dATP to the corresponding rADP or dADP and P(i). H6-G2P interacts with two discrete G1P domains (I and II). Full-length G1P and G1PDeltaN62 (lacking domain I) stimulate 3.5- and 1.9-fold, respectively, the ATPase activity of H6-G2P. The results presented suggest that a DNA structure, artificially promoted by distamycin A or facilitated by the assembly of G1P at pacL and/or pacR, stimulates H6-G2P cleavage at both target sites within pacC. In the presence of two G1P decamers per H6-G2P monomer, the H6-G2P endonuclease is repressed, and the ATPase activity stimulated. Based on these results, we propose a model that can account for the role of terminase in headful packaging.

[Bone scintigraphy findings in patients with recently diagnosed adenocarcinoma of the prostate: relationship with prostate specific antigen levels]

BACKGROUND AND OBJECTIVES

Although it has been suggested that bone scintigraphy (BS) may not be necessary in patients with prostate adenocarcinoma (PA) and normal prostate specific antigen (PSA) plasma levels, controversy still remains. The objective of the study was to evaluate the existing relationship between PSA plasma levels and BS findings in patients with a recently diagnosed PA in order to assess whether BS may be omitted on the basis of the PSA levels in these patients.

METHODS

The 475 patients (70+/-7 years old) consecutively diagnosed of PA between 1994 and 1998 in our institution made up the study population. PSA plasmatic levels were determined and BS was performed (body planar study after 99mTc-methyl diphosphonate 900 MBq administration) in all the patients.

RESULTS

In 362 patients (76.2%), BS was negative, in 108 (22.7%) positive and undetermined in the remaining 5 patients (1.1%). The mean PSA level in the whole study population was 74+/-267 ng/ml (range 0.4-4.200) and was higher in patients with positive GO (218+/-512 vs 31+/-89, p<0,0001). As PSA increased, the rate of patients with positive BS was significantly higher, this being 0%, 16.4%, 9.7%, 14.0%, 31.0% and 48.3% in patients with PSA 4, 4.1-10; 10.1-20; 20.1-30; 30.1-40, and >40 ng/ml, respectively (p<0.0001). In patients with positive BS, the PSA levels were 20 and 10 ng/ml in 30.6% and 18.6% of the patients, respectively.

CONCLUSION

According to our experience, there is a significant association between PSA plasma levels and the BS results in patients with recently diagnosed PA. However, a significant proportion of patients with bone metastasis have normal PSA levels, and therefore BS should be performed in all patients with recently diagnosed PA regardless of the PSA levels.

[Results of myocardial scintigraphy with 99mTc-tetrofosmin and dipyridamole administration in patients diagnosed of microvascular angina]

The objective of the study was to evaluate the results of the myocardial scintigraphy with 99mTc-tetrofosmin (Tc-Tf) and pharmacological stimulation with dipyridamole in patients diagnosed of microvascular angina. The study population is made up of 50 patients discharged with the diagnosis of microvascular angina who had undergone Tc-Tf-dipyridamole. Clinical and electrical positivity appeared in 40% and 12% of the patients, respectively. Myocardial perfusion defects were found in 35 patients (70%), and were reversible in 21 (60%), fixed in 11 (21%), and combined in 3 (9%). Abnormalities were inferior, anteroseptal and lateral in 21, 18, and 2 patients, respectively. Patients with a positive exercise treadmill test, compared with those with a negative one, had more frequent perfusion abnormalities (91% vs 50%, p = 0.0327) and myocardial ischemia (64% vs 20%, p = 0.392). Women, in comparison with men, had angina (56% vs 22%, p = 0.013), and anteroseptal perfusion abnormalities (26% vs 4%, p = 0.028) more frequently. On the contrary, men had inferior perfusion abnormalities more frequently (57% vs 30%, p = 0.057). Thus, Tc-Tf-dipyridamole shows perfusion abnormalities in 70% of patients with microvascular angina (91% in patients with a positive exercise treadmill test). Scintigraphic pattern may be partially conditioned by gender in these patients.

Population subdivision in Europe's great bustard inferred from mitochondrial and nuclear DNA sequence variation

A continent-wide survey of sequence variation in mitochondrial (mt) and nuclear (n) DNA of the endangered great bustard (Otis tarda) was conducted to assess the extent of phylogeographic structure in a morphologically monotypic bird. DNA sequence variation in a combined 809 bp segment of the mtDNA genome from 66 individuals from the last six breeding regions showed relatively low levels of intraspecific sequence diversity (n = 0.32%) but significant differences in the regional distribution of 11 haplotypes (phiST = 0.49). Despite their exceptional potential for dispersal, a complete and long-term historical separation between the populations from the Iberian Peninsula (Spain) and mainland Europe (Hungary, Slovakia, Germany, and Russia) was demonstrated. Divergence between populations based on a 3-bp insertion-deletion polymorphism within the intron region of the nuclear CHD-Z gene was geographically concordant with the primary subdivision identified within the mtDNA sequences. Inferred aspects of phylogeography were used to formulate conservation recommendations for this endangered species.

Bacillus subtilis homologous recombination: genes and products

Homologous recombination plays a critical role in maintaining gene diversification and genome stability. Fourteen Bacillus subtilis recombination gene products have been genetically characterised and classified into five different epistatic groups. At least seven other recombination genes could be predicted. Recombination gene products which define activities that help RecA to process DNA repair and recombination have been studied, but those that processed recombination intermediates into products (post-synaptic stage) await elucidation.

Generation of food-grade recombinant lactic acid bacterium strains by site-specific recombination

The construction of a delivery and clearing system for the generation of food-grade recombinant lactic acid bacterium strains, based on the use of an integrase (Int) and a resolvo-invertase (beta-recombinase) and their respective target sites (attP-attB and six, respectively) is reported. The delivery system contains a heterologous replication origin and antibiotic resistance markers surrounded by two directly oriented six sites, a multiple cloning site where passenger DNA could be inserted (e.g., the cI gene of bacteriophage A2), the int gene, and the attP site of phage A2. The clearing system provides a plasmid-borne gene encoding beta-recombinase. The nonreplicative vector-borne delivery system was transformed into Lactobacillus casei ATCC 393 and, by site-specific recombination, integrated as a single copy in an orientation- and Int-dependent manner into the attB site present in the genome of the host strain. The transfer of the clearing system into this strain, with the subsequent expression of the beta-recombinase, led to site-specific DNA resolution of the non-food-grade DNA. These methods were validated by the construction of a stable food-grade L. casei ATCC 393-derived strain completely immune to phage A2 infection during milk fermentation.

Shape and DNA packaging activity of bacteriophage SPP1 procapsid: protein components and interactions during assembly

The procapsid of the Bacillus subtilis bacteriophage SPP1 is formed by the major capsid protein gp13, the scaffolding protein gp11, the portal protein gp6, and the accessory protein gp7. The protein stoichiometry suggests a T=7 symmetry for the SPP1 procapsid. Overexpression of SPP1 procapsid proteins in Escherichia coli leads to formation of biologically active procapsids, procapsid-like, and aberrant structures. Co-production of gp11, gp13 and gp6 is essential for assembly of procapsids competent for DNA packaging in vitro. Presence of gp7 in the procapsid increases the yield of viable phages assembled during the reaction in vitro five- to tenfold. Formation of closed procapsid-like structures requires uniquely the presence of the major head protein and the scaffolding protein. The two proteins interact only when co-produced but not when mixed in vitro after separate synthesis. Gp11 controls the polymerization of gp13 into normal (T=7) and small sized (T=4?) procapsids. Predominant formation of T=7 procapsids requires presence of the portal protein. This implies that the portal protein has to be integrated at an initial stage of the capsid assembly process. Its presence, however, does not have a detectable effect on the rate of procapsid assembly during SPP1 infection. A stable interaction between gp6 and the two major procapsid proteins was only detected when the three proteins are co-produced. Efficient incorporation of a single portal protein in the procapsid appears to require a structural context created by gp11 and gp13 early during assembly, rather than strong interactions with any of those proteins. Gp7, which binds directly to gp6 both in vivo and in vitro, is not necessary for incorporation of the portal protein in the procapsid structure.

Plasmid copy-number control and better-than-random segregation genes of pSM19035 share a common regulator

Transcription initiation of the copy-number control and better-than-random segregation genes of the broad-host-range and low-copy-number plasmid pSM19035 are subjected to repression by the autoregulated pSM19035-encoded omega product in Bacillus subtilis cells. The promoters of the copS (Pcop1 and Pcop2), delta (Pdelta), and omega (Pomega) genes have been mapped. These promoters are embedded in a set of either seven copies of a 7-bp direct repeat or in a block consisting of two 7-bp direct repeats and one 7-bp inverted repeat; the blocks are present either two or three times. The cooperative binding of omega protein to the repeats on the Pcop1, Pcop2, Pdelta, and Pomega promoters represses transcription initiation by a mechanism that does not exclude sigma(A)RNAP from the promoters. These results indicate that omega protein regulates plasmid maintenance by controlling the copy number on the one hand and by regulating the amount of proteins required for better-than-random segregation on the other hand.

Crystallization and preliminary X-ray diffraction studies of Streptococcus pyogenes plasmid pSM19035-encoded omega transcriptional repressor

The transcriptional repressor, omega protein, from the Streptococcus pyogenes broad-host-range plasmid pSM19035 was crystallized at pH 7. 5 and 8.5 by the vapour-diffusion method using PEG 4000 as precipitant. Two crystal forms were obtained; the first belongs to the tetragonal space group P4(1)2(1)2 or P4(3)2(1)2 and the second to the hexagonal space group P6(1) or P6(5). The crystals are most likely to contain one omega protein in the asymmetric unit, with V(m) values of 3.2 and 3.5 A(3) Da(-1), respectively. The crystals diffract X-rays to 2.4 and 2.9 A resolution for the tetragonal and hexagonal systems, -respectively.

A2 cro, the lysogenic cycle repressor, specifically binds to the genetic switch region of Lactobacillus casei bacteriophage A2

Lysogenic induction of temperate bacteriophage A2 of Lactobacillus casei is controlled by the action of its cI and cro products at the phage operator region. Three 20-bp inverted repeated DNA segments (subsites O1, O2, and O3) and the two divergent (PL and PR) promoters were mapped within the 153-bp operator region. The A2-encoded Cro product is shown to be the functional homolog of lambda Cro. The binding of Cro to the three operator subsites is noncooperative and yields two discrete protein-DNA complexes of retarded migration in mobility shift assays. The Kapp value for the Cro-PL-PR DNA complex was estimated to be 6 nM. Cro shows a slightly higher affinity for O3 than for O1 and O2 subsites. The O3 subsite overlaps the -35 hexamer of the PL promoter, which directs cI expression. A Cro mutant protein, devoid of the last 12 residues (Cro*), allowed the assignment of the DNA-binding domain to the NH2 end of Cro. The C end enhances its affinity for the DNA and probably stabilizes bending induced by Cro.

Technetium-99m-HMPAO-labeled leukocyte imaging in patients with seronegative spondyloarthropathies

OBJECTIVE

Gut inflammation is frequent among patients with seronegative spondyloarthropathies (SSp). The purpose of this study was to evaluate the presence of positive abdominal findings in patients with SSp who did not have clinical symptoms or signs of inflammatory bowel disease (IBD). This represents a new indication for abdominal 99mTc-HMPAO-labeled leukocyte scintigraphy.

METHODS

Eighty-six patients (59 with SSp and 27 controls) were prospectively imaged with 99mTc-HMPAO-labeled leukocytes.

RESULTS

Leukocyte imaging was positive in 33 patients with SSp (56%), 27 of these patients scored between 2+ and 4+ (51%). Four (15%) control patients also had positive findings.

CONCLUSION

These findings provide evidence linking SSp with intestinal inflammation. SSp may be an important new indication for 99mTc-HMPAO-labeled autologous leukocyte scintigraphy.

Cooperative interaction of CI protein regulates lysogeny of Lactobacillus casei by bacteriophage A2

The temperate bacteriophage A2 forms stable lysogens in Lactobacillus casei. The A2-encoded cI product (CI), which is responsible for maintaining the A2 prophage in the lysogenic state, has been purified. The CI protein, which is a monomer of 25.3 kDa in solution, specifically binds to a 153-bp DNA fragment that contains two divergent promoters, PL and PR. These promoters mediate transcription from cI and a putative cro, respectively. Three similar, although not identical, 20-bp inverted repeated DNA segments (operator sites O1, O2, and O3) were found in this segment. CI selectively interacts with O1, which is placed downstream from the transcription start point of the cro gene, and with O2 and O3, which overlap with the -35 region of the two promoters. Using a heterologous RNA polymerase, we have determined the transcription start points of PL and PR. CI exerts a negative effect on the in vitro transcription of PR by repositioning the RNA polymerase in a concentration-dependent manner. CI, when bound to O1 and O2, enhances the positioning of the RNA polymerase with the PL promoter. Our data indicate that the CI protein regulates the lytic and lysogenic pathways of the A2 phage.

Proteolytic cleavage of gram-positive beta recombinase is required for crystallization

Beta recombinase, a DNA resolvase-invertase, catalyzes in the presence of a chromatin-associated protein such as Hbsu, DNA resolution or DNA inversion on supercoiled substrates containing two directly or inversely oriented target (six) sites. Single crystals of the beta recombinase from plasmid pSM19035 were obtained using the vapor diffusion technique with ammonium phosphate as the precipitating agent. The crystals diffracted X-rays to a maximum resolution of 2.5A. Due to proteolytic degradation during the crystallization experiment, the crystals contain only the N-terminal catalytic domain of beta recombinase corresponding to about 60% of the molecular mass of the initially assayed native protein. The proteolytic removal of the C-terminal DNA-binding domain demonstrated that protein modification can be essential to provide material suitable for X-ray analysis.

Bacillus subtilis sequence-independent DNA-binding and DNA-bending protein Hbsu negatively controls its own synthesis

Transcription of the hbs gene under vegetative growth condition is subject to repression when cells enter in late exponential phase. We have determined the sites at which transcription of the hbs gene initiates in vitro. On a supercoiled template, transcription of the hbs gene is initiated by sigmaARNAP at two overlapping hbs promoters (P1 and P3). We have demonstrated that highly purified Hbsu protein acts as a repressor of its own synthesis. The binding of the sequence-independent DNA-binding and DNA-bending Hbsu protein does not seem to exclude sigmaARNAP from the promoters. In this report we show that Hbsu, in vitro, does not repress transcription by a mere steric hindrance on sigmaARNAP binding.

The Bacillus subtilis bacteriophage SPP1 G39P delivers and activates the G40P DNA helicase upon interacting with the G38P-bound replication origin

Initiation of Bacillus subtilis bacteriophage SPP1 replication requires the phage-encoded genes 38, 39 and 40 products (G38P, G39P and G40P). G39P, which does not bind DNA, interacts with the replisome organiser, G38P, in the absence of ATP and with the ATP-activated hexameric replication fork helicase, G40P. G38P, which specifically interacts with the phage replication origin (oriL) DNA, does not seem to form a stable complex with G40P in solution. G39P when complexed with G40P-ATP inactivates the single-stranded DNA binding, ATPase and unwinding activities of G40P, and such effects are reversed by increasing amounts of G38P. Unwinding of a forked substrate by G40P-ATP is increased about tenfold by the addition of G38P and G39P to the reaction mixture. The specific protein-protein interactions between oriL-bound G38P and the G39P-G40P-ATPgammaS complex are necessary for helicase delivery to the SPP1 replication origin. Formation of G38P-G39P heterodimers releases G40P-ATPgammaS from the unstable oriL-G38P-G39P-G40P-ATPgammaS intermediate. G40P-ATPgammaS binds to the origin region, the uncomplexed G38P fraction remains bound to oriL, and the G38P-G39P heterodimer is lost from the complex. We demonstrate that G39P is a component of an oligomeric nucleoprotein complex which plays an important role in the initiation of SPP1 replication.

Analysis of the Bacillus subtilis recO gene: RecO forms part of the RecFLOR function

The deduced protein product of the Bacillus subtilis gene yqfI, which is 255 residues long, shares homology (25% identity) with the Escherichia coli RecO protein. A null allele of yqfI, when present in an otherwise Rec+ B. subtilis strain, causes cells to become highly sensitive to DNA-damaging agents, and plasmid transformation (intramolecular recombination) is reduced by 25-fold while chromosomal transformation (intermolecular recombination) is only moderately affected (2.5-fold reduction). Therefore, the yqfI gene was renamed recO and its null allele is referred to as recO1. The recO1 mutation was introduced into recombination-deficient strains representative of the epistatic groups alpha (recF, recR and recL strains), beta (addA5 addB72), gamma (recH342) and epsilon (recU40). The recO mutation did not affect the sensitivity of recF, recR or recL cells to DNA-damaging agents, increased the sensitivity of recU and addAB cells and abolished the DNA repair capacity of recH cells. The recO mutation did not affect intermolecular recombination in recF, recL, recH or recU cells, but reduced (by about 9-fold) the incidence of intermolecular recombination in addAB cells. The recO mutation did not affect intramolecular recombination in the addAB, recU, recF or recL cells, but reduced it by about 75-fold in recH cells. The defects caused by the recO1 mutation can be partially suppressed by a common suppressor of the recF, recL and recR phenotypes. We therefore assigned recO to epistatic group alpha and predict that the RecO protein acts at the same stage of recombination as the RecF, RecL and RecR proteins, in a RecFLOR complex.

The prokaryotic beta-recombinase catalyzes site-specific recombination in mammalian cells

The development of new strategies for the in vivo modification of eukaryotic genomes has become an important objective of current research. Site-specific recombination has proven useful, as it allows controlled manipulation of murine, plant, and yeast genomes. Here we provide the first evidence that the prokaryotic site-specific recombinase (beta-recombinase), which catalyzes only intramolecular recombination, is active in eukaryotic environments. beta-Recombinase, encoded by the beta gene of the Gram-positive broad host range plasmid pSM19035, has been functionally expressed in eukaryotic cell lines, demonstrating high avidity for the nuclear compartment and forming a clear speckled pattern when assayed by indirect immunofluorescence. In simian COS-1 cells, transient beta-recombinase expression promoted deletion of a DNA fragment lying between two directly oriented specific recognition/crossing over sequences (six sites) located as an extrachromosomal DNA substrate. The same result was obtained in a recombination-dependent lacZ activation system tested in a cell line that stably expresses the beta-recombinase protein. In stable NIH/3T3 clones bearing different number of copies of the target sequences integrated at distinct chromosomal locations, transient beta-recombinase expression also promoted deletion of the intervening DNA, independently of the insertion position of the target sequences. The utility of this new recombination tool for the manipulation of eukaryotic genomes, used either alone or in combination with the other recombination systems currently in use, is discussed.

Bacillus subtilis DnaG primase stabilises the bacteriophage SPP1 G40P helicase-ssDNA complex

Purified Bacillus subtilis DnaG primase (predicted molecular mass 68.8 kDa) behaves as a monomer in solution. We demonstrate that DnaG physically interacts with bacteriophage SPP1 hexameric helicase G40P (G40P6) in the absence of ATP. G40P6-ATP forms an unstable complex with ssDNA, and by itself carries out ATP-driven translocation along a ssDNA template with low processivity. The presence of DnaG in the reaction mixture increased the helicase activity of G40P6 about 3-fold, but not the ATPase activity. The results presented here suggest that the DnaG protein stabilises the G40P6-ssDNA complexes.