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PubMed1998

Retroviral recombination rates do not increase linearly with marker distance and are limited by the size of the recombining subpopulation.

Recombination occurs at high frequencies in all examined retroviruses. The previously determined homologous recombination rate in one retroviral replication cycle is 4% for markers 1.0 kb apart in spleen necrosis virus (SNV). This has often been used to suggest that approximately 30 to 40% of the replication-competent viruses with 7- to 10-kb genomes undergo recombination. These estimates were based on the untested assumption that a linear relationship exists between recombination rates and marker distances. To delineate this relationship, we constructed three sets of murine leukemia virus (MLV)-based vectors containing the neomycin phosphotransferase gene (neo) and the hygromycin phosphotransferase B gene (hygro). Each set contained one vector with a functional neo and an inactivated hygro and one vector with a functional hygro and an inactivated neo. The two inactivating mutations in the three sets of vectors were separated by 1.0, 1.9, and 7.1 kb. Recombination rates after one round of replication were 4.7, 7.4, and 8.2% with markers 1.0, 1.9, and 7.1 kb apart, respectively. Thus, the rate of homologous recombination with 1.0 kb of marker distance is similar in MLV and SNV. The recombination rate increases when the marker distance increases from 1.0 to 1.9 kb; however, the recombination rates with marker distances of 1.9 and 7.1 kb are not significantly different. These data refute the previous assumption that recombination is proportional to marker distance and define the maximum recombining population in retroviruses.

Genome, Viral↗
PubMed2002

In vitro intersubtype recombinants of human immunodeficiency virus type 1: comparison to recent and circulating in vivo recombinant forms.

The increased prevalence of human immunodeficiency virus type 1 (HIV-1) intersubtype recombinants (ISRs) is shaping HIV-1 evolution throughout the world and will have an impact on both therapeutic and vaccine strategies. This study was designed to generate and compare in vitro ISRs to those isolated from HIV-infected individuals throughout the world. Human peripheral blood mononuclear cells were dually infected with seven pairs of HIV-1 isolates from different subtypes (i.e., A to F). Recombinant crossover sites were mapped to specific regions in the envelope (env) gene by using a cloning-hybridization technique and subtype-specific probes. In vitro intersubtype recombination was at least twofold more frequent in the V1-to-V3 region than in any other env fragment, i.e., C1 to V1, V3 to V5, or V5 to gp41. Sequence and recombination site analyses suggested the C2 env domain as a "hot region" for recombination and selection of replication-competent ISRs during the 15-day incubation. In addition to these regional preferences for env recombination, homopolymeric nucleotide tracts, i.e., sequences known to pause reverse transcriptase and promote template switching, were found in most in vitro crossover sites. ISRs, originating from recent dual infections and limited transmission events, partly retained this in vitro regional or sequence preference for recombination sites. However, a shift to crossover sites flanking the gp120-coding sequence was evident in the stable circulating recombinant forms of HIV-1. Based on these findings, HIV-1 recombinants generated from these dual infections may be used as a model for in vivo intersubtype recombination and for the design of various diagnostic assays and vaccine constructs.

Base Sequence↗
PubMed1992

Single-stranded DNA as a recombination substrate in plants as assessed by stable and transient recombination assays.

Two separate assays, one that requires stable integration of recombination products and one that does not, were employed to elucidate the role of single-stranded DNA in extrachromosomal homologous recombination in Nicotiana tabacum. Both assays revealed that single-stranded DNA in linear and in circular forms was an efficient substrate for recombination, provided that the cotransformed recombination substrates were of complementary sequence, so that direct annealing was possible. Recombination was inefficient when both single-stranded recombination partners contained homologous regions of identical sequence and generation of a double-stranded DNA was required prior to heteroduplex formation. These results indicate that direct annealing of single strands is an important initial step for intermolecular recombination in tobacco cells. Annealed cotransformed single-stranded molecules yielded intermediates that could be further processed by either continuous or discontinuous second-strand synthesis. The type of intermediate had no influence on the recombination efficiency. Double-stranded circles were unable to recombine efficiently either with each other or with single-stranded DNA. Our results suggest that a helicase activity is involved in the initial steps of double-stranded DNA recombination which unwinds duplex molecules at the site of double-strand breaks.

Base Sequence↗
PubMed2005

Recombination every day: abundant recombination in a virus during a single multi-cellular host infection.

Viral recombination can dramatically impact evolution and epidemiology. In viruses, the recombination rate depends on the frequency of genetic exchange between different viral genomes within an infected host cell and on the frequency at which such co-infections occur. While the recombination rate has been recently evaluated in experimentally co-infected cell cultures for several viruses, direct quantification at the most biologically significant level, that of a host infection, is still lacking. This study fills this gap using the cauliflower mosaic virus as a model. We distributed four neutral markers along the viral genome, and co-inoculated host plants with marker-containing and wild-type viruses. The frequency of recombinant genomes was evaluated 21 d post-inoculation. On average, over 50% of viral genomes recovered after a single host infection were recombinants, clearly indicating that recombination is very frequent in this virus. Estimates of the recombination rate show that all regions of the genome are equally affected by this process. Assuming that ten viral replication cycles occurred during our experiment-based on data on the timing of coat protein detection-the per base and replication cycle recombination rate was on the order of 2 x 10(-5) to 4 x 10(-5). This first determination of a virus recombination rate during a single multi-cellular host infection indicates that recombination is very frequent in the everyday life of this virus.

Caulimovirus↗
PubMed1975

[Recombination of mitochondrial markers in yeasts. I. Analysis of isomitochondrial crosses and a study of the influence of locus determining mating type on recombination].

Yeast mitochondrial markers of the resistance to antibiotics (erythromycin, neomycin and monomycin) were used to study mitochondrial recombination in bifactorial crosses both in cis and trans configurations of markers. Our strains of Saccharomyces cerevisiae are isochromosomal and isomitochondrial due to all of them have originated from one haploid pace XII of Sacch. cerevisiae. The following parameters of mitochondrial recombination were examined in random samples of zygotic diploid daughter colonies; a) the asymmetric transmission of parental classes; b) the frequency of recombination; c) the polarity of recombination; d) the effect of cell mating type on these parameters in reciprocal crosses. The data obtained suggest the following features of mitochondrial recombination: a) The distribution of both classes as parental and recombinant is unequal: there is asymmetrical transmission (0,22-1,72) and some polarity of recombination (up to 4,0). b) The effect of cell mating type on asymmetrical transmission was established only is some crosses in trans-configuration of mitochondrial markers. In cis-configuration crosses such effect was not observed. c) Different mitochondrial mutations influenced on all the above listed parameters (asymmetrical transmission of parental classes, the frequency and the polarity of recombination). Some correlation between the high level of asymmetrical transmission of parental classes and the low frequency of recombination was found in crosses with NR and MR mutants. The existence of several different loci among ER, NR and MR mutants is suggested on the basis of the data on the recombination frequency.

Anti-Bacterial Agents↗
PubMedDate not supplied

Diversified prime and boost protocols using recombinant vaccinia virus and recombinant non-replicating avian pox virus to enhance T-cell immunity and antitumor responses.

Recombinant vaccinia viruses containing tumor associated genes represent an attractive vector to induce immune responses to weak immunogens in cancer immunotherapy protocols. The property of intense immunogenicity of vaccinia proteins, however, also serves to limit the number of inoculations of recombinant vaccinia viruses. Host immune responses to the first immunization have been shown to limit the replication of subsequent vaccinations and thus reduce effectiveness of boost inoculations. The use of recombinant avian pox viruses (avipox) such as the canarypox (ALVAC) or fowlpox are potential candidates for immunization protocols in that they can infect mammalian cells and express the inserted transgene, but do not replicate in mammalian cells. We report here the construction and characterization of a canarypox (ALVAC) recombinant expressing the human carcinoembryonic antigen (CEA) gene (designated ALVAC-CEA). Antibody, lymphoproliferative and cytolytic T-cell responses as well as tumor inhibition were shown to be elicited by the ALVAC-CEA recombinant in a murine model. The utilization of a diversified immunization scheme using a recombinant vaccinia virus followed by recombinant avian pox virus was shown to be far superior than the use of either one alone in eliciting CEA-specific T-cell responses. Experiments were conducted to determine if the use of a diversified immunization scheme using a recombinant vaccinia virus (rV-CEA) and ALVAC-CEA would be superior to the use of either one alone in eliciting CEA-specific T-cell responses. When mice were immunized with rV-CEA and then ALVAC-CEA. CEA-specific T-cell responses were at least four times greater, and for superior to those achieved with three immunizations of ALVAC-CEA. Multiple boosts of ALVAC-CEA following rV-CEA immunization further potentiated anti-tumor effects and CEA specific T-cell responses. These studies demonstrate the proof of concept of the advantage of diversified immunization protocols employing both recombinant vaccinia and recombinant avipox vectors.

Adenocarcinoma↗
PubMed1999

Effect of virulence on immunogenicity of single and double vaccinia virus recombinants expressing differently immunogenic antigens: antibody-response inhibition induced by immunization with a mixture of recombinants differing in virulence.

It has been shown recently that the residual virulence of vaccinia virus (VV) is an important factor that influences the outcome of immunization with VV recombinants. This study focused on the correlation of the residual virulence of several VV recombinants with antibody responses against the strongly immunogenic extrinsic glycoprotein E of varicella-zoster virus and the weakly immunogenic extrinsic protein preS2-S of hepatitis B virus and against VV proteins, with mice used as a model organism. Furthermore, the effects of mixing different recombinants on the antibody response were studied. The results obtained indicated that: (i) the antibody response depended on the residual virulence of the recombinants, more so in the case of the weakly immunogenic protein; (ii) the residual virulence, the growth rate of the VV recombinants in extraneural tissues and the immunogenicity were associated features; (iii) immunization with mixtures of two differently virulent recombinants or with unequal amounts of two similarly virulent recombinants sometimes led to the suppression of antibody response. The appearance of this suppression was dependent on three factors: the residual virulence of the recombinants, the immunogenicity of the extrinsic proteins and the ratio of the recombinants in the mixtures. Thus, the data obtained demonstrate that there are various limitations to the use of replicating VV recombinants for immunization purposes.

Animals↗
PubMed1996

Characterization of a mutant RecA protein that facilitates homologous genetic recombination but not recombinational DNA repair: RecA423.

A recA mutant (recA423; Arg169-->His), with properties that should help clarify the relationship between the biochemical properties of RecA protein and its two major functions, homologous genetic recombination and recombinational DNA repair, has been isolated. The mutant has been characterized in vivo and the purified RecA423 protein has been studied in vitro. The recA423 cells are nearly as proficient in conjugational recombination, transductional recombination, and recombination of lambda red- gam- phage as wild-type cells. At the same time, the mutant cells are deficient for intra-chromosomal recombination and nearly as sensitive to UV irradiation as a recA deletion strain. The cells are proficient in SOS induction, and results indicate the defect involves the capacity of RecA protein to participate directly in recombinational DNA repair. In vitro, the RecA423 protein binds to single-stranded DNA slowly, with an associated decline in the ATP hydrolytic activity. The RecA423 protein promoted a limited DNA strand exchange reaction when the DNA substrates were homologous, but no bypass of a short heterologous insert in the duplex DNA substrate was observed. These results indicate that poor binding to DNA and low ATP hydrolysis activity can selectively compromise certain functions of RecA protein. The RecA423 protein can promote recombination between homologous DNAs during Hfr crosses, indicating that the biochemical requirements for such genetic exchanges are minimal. However, the deficiencies in recombinational DNA repair suggest that the biochemical requirements for this function are more exacting.

Adenosine Triphosphatases↗
PubMed1996

Immobilized hirudin and hirudin-based peptides used for the purification of recombinant human thrombin prepared from recombinant human prothrombin.

A simple and efficient activation-affinity purification system was developed to obtain thrombin from recombinant CHO cells expressing human prothrombin. In this method, a controllable process for the activation of recombinant prothrombin is directly coupled with a purification strategy for the recombinant thrombin generated. At a constant flow rate and with a contact time limited to few seconds, recombinant prothrombin was filtered through immobilized trypsin. In a closed flow system, the recombinant thrombin generated was filtered through newly designed thrombin-specific affinity gels. Hirudin, the most specific thrombin inhibitor, and hirudin-based peptides were covalently immobilized to Sepharose, thus creating thrombin-specific affinity gels that immediately absorb the thrombin generated from the activation mixture. Prothrombin and incompletely activated molecules did not bind to the affinity gel and were recirculated for a further activation cycle. Due to the specificity of the affinity gels for thrombin and the elimination of thrombin from the activation mixture, proteolytic degradation and autocatalytic inactivation of the recombinant thrombin was prevented. Recombinant thrombin was isolated from the hirudin-based affinity gels by chaotrope salt elution, resulting in high yields of highly pure, active thrombin. Affinity purification of thrombin was not deleteriously affected by contamination of the starting material with other proteins. Activation and affinity purification were equally effective for recombinant and human plasma-derived prothrombin as well as for human and recombinant thrombin.

Amino Acid Sequence↗
PubMed2006

Global transcriptome response of recombinant Escherichia coli to heat-shock and dual heat-shock recombinant protein induction.

Recombinant Escherichia coli cultures are used to manufacture numerous therapeutic proteins and industrial enzymes, where many of these processes use elevated temperatures to induce recombinant protein production. The heat-shock response in wild-type E. coli has been well studied. In this study, the transcriptome profiles of recombinant E. coli subjected to a heat-shock and to a dual heat-shock recombinant protein induction were examined. Most classical heat-shock protein genes were identified as regulated in both conditions. The major transcriptome differences between the recombinant and reported wild-type cultures were heavily populated by hypothetical and putative genes, which indicates recombinant cultures utilize many unique genes to respond to a heat-shock. Comparison of the dual stressed culture data with literature recombinant protein induced culture data revealed numerous differences. The dual stressed response encompassed three major response patterns: induced-like, in-between, and greater than either individual stress response. Also, there were no genes that only responded to the dual stress. The most interesting difference between the dual stressed and induced cultures was the amino acid-tRNA gene levels. The amino acid-tRNA genes were elevated for the dual cultures compared to the induced cultures. Since, tRNAs facilitate protein synthesis via translation, this observed increase in amino acid-tRNA transcriptome levels, in concert with elevated heat-shock chaperones, might account for improved productivities often observed for thermo-inducible systems. Most importantly, the response of the recombinant cultures to a heat-shock was more profound than wild-type cultures, and further, the response to recombinant protein induction was not a simple additive response of the individual stresses.

Cell Culture Techniques↗
PubMed1985

Phage P1 Cre-loxP site-specific recombination. Effects of DNA supercoiling on catenation and knotting of recombinant products.

Bacteriophage P1 contains a site-specific recombination system consisting of a site, loxP, and a recombinase protein Cre. We have shown that with purified Cre protein we can carry out recombination between two loxP sites in vitro. When that recombination occurs between two sites in direct orientation on the same DNA molecule, we observed the production of free and catenated circular molecules. In this paper we show that recombination between sites in opposite orientation leads to both knotted and unknotted circular products. We also demonstrate that the production of catenanes and knots is influenced by two factors: (1) supercoiling in the DNA substrate, supercoiled DNA substrates yield significantly more catenated and knotted products than nicked circular substrates; and (2) mutations in the loxP site, a class of mutations have been isolated that carry out recombination but result in a distribution of products in which the ratio of catenanes to free circles is increased over that observed with a wild-type site. A more detailed analysis of the products from recombination between wild-type sites indicates: (1) that the catenanes or knots produced by recombination are both simple and complex; (2) that the ratio of free products to catenanes is independent of the distance between the two directly repeated loxP sites; and (3) that for DNA substrates with four loxP sites significant recombination between non-adjacent sites occurs to give free circular products. These observations provide insights into how two loxP sites are brought together during recombination.

Bacteriophages↗
PubMed1986

The primary structure of crossover regions of intertypic poliovirus recombinants: a model of recombination between RNA genomes.

The nucleotide sequence of crossover sites in the genome of four intertypic (type 3/type 1) poliovirus recombinants has been determined. The approximate boundaries of the crossover regions were first estimated by RNase T1 oligonucleotide mapping of the recombinant genomes; then appropriate regions were sequenced by the chain termination method using oligonucleotide-primed reverse transcription of the recombinant RNAs. The crossover sites (defined as the contiguous sequences shared by the recombinant and both parental genomes flanked, in the recombinant genome, by heterotypic RNA segments) are 5, 5, 7, and 11 nucleotides long, respectively. The recombination was precise and was not accompanied by any other genetic alterations. The recombination sites were found to be located within genome segments having a potential to form secondary structure elements. Based on this observation, a model of recombination between picornaviral RNA genomes has been proposed. The essence of this model consists in bringing together homologous regions of two recombining RNA genomes via formation of intermolecular duplexes, detachment of the nascent 3' end of the newly synthesized complementary RNA from a "parting" site on the first template and its subsequent "jumping" to the identical (or closely related) "anchoring" site on the other template. Features of this model are discussed in some detail.

Base Sequence↗
PubMed1982

Illegitimate recombination mediated in vitro by DNA gyrase of Escherichia coli: structure of recombinant DNA molecules.

We have developed a cell-free system from Escherichia coli for studying illegitimate recombination between nonhomologous DNA molecules. The recombination is stimulated by oxolinic acid, an inhibitor of DNA gyrase. The stimulation is abolished by coumermycin A1 and is not found in extracts of nalidixic acid-resistant (gyrA) mutants. We therefore inferred that DNA gyrase directly participates in illegitimate recombination, at least in the presence of oxolinic acid [Ikeda, H., Moriya, K. & Matsumoto, T. (1981) Cold Spring Harbor Symp. Quant. Biol. 45, 399--408]. The structure of recombinant DNA molecules formed in the presence of oxolinic acid from a cross between phage lambda and plasmid pBR322 DNAs was analyzed by heteroduplex mapping. Among nine isolates tested, two recombinants were formed by the insertion of the plasmid into the lambda genome. The seven other recombinants had more complicated genome structures. Insertion of pBR322 was accompanied by a deletion on one of the genomes. In all cases, the end points of deletions coincided with one end of the pBR322 insertion. Recombination sites seemed to be distributed randomly on the lambda and pBR322 genomes. Analysis of nucleotide sequences of the recombination junctions proved that the crossover took place between nonhomologous DNA sequences. A model for DNA gyrase-mediated illegitimate recombination is discussed.

Bacteriophage lambda↗
PubMed1992

Replication inhibition by nucleoside analogues of a recombinant Autographa californica multicapsid nuclear polyhedrosis virus harboring the herpes thymidine kinase gene driven by the IE-1(0) promoter: a new way to select recombinant baculoviruses.

The expression of the thymidine-thymidylate kinase (HSV1-TK), (ATP: thymidine 5'-phosphotransferase; EC 2.7.1.21) of herpes simplex virus type 1 endows the host cell with a conditional lethal phenotype which depends on the presence of nucleoside analogues metabolized by this enzyme into toxic inhibitors of DNA replication. To generate a recombinant baculovirus that could be selected against by nucleoside analogs, the HSV1-tk coding sequence was placed under the control of the Autographa californica multicapsid nuclear polyhedrosis virus (AcMNPV) immediate early promoterm IE-1(0), and this construction was introduced via homologous recombination into the polyhedrin locus of AcMNPV. Two recombinant baculoviruses harboring this gene construct at the polyhedrin locus were isolated and tested for their ability to replicate in the presence of various concentrations of the nucleoside analog 9-(1,3-Dihydroxy-2-propoxymethyl)guanine (Ganciclovir). Neither Sf9 lepidopteran cell viability nor replication of wild type or beta-Galactosidase-expressing recombinant AcMNPVs were affected by concentrations of Ganciclovir up to 100 microM. In contrast, replication of the recombinant AcMNPV virus harboring the HSV1-tk gene was inhibited by Ganciclovir in a dose-dependent manner. The inhibition was detectable at 2 microM and complete at 100 microM. This property was exploited in model isolations aimed at purifying new recombinant viruses having lost this counter-selectable gene marker as a result of homologous recombination at the polyhedrin locus after cotransfection of the viral DNA with a replacement vector. After being propagated in the presence of Ganciclovir, the progeny of such co-transfections contained over 85% recombinant viruses, demonstrating that counter-selection of parental HSV1-tk-containing viruses by Ganciclovir constitutes a novel approach for recombinant baculovirus isolation.

Animals↗
PubMed2007

Patterns of recombination in turnip mosaic virus genomic sequences indicate hotspots of recombination.

Potyviruses have variable single-stranded RNA genomes and many show clear evidence of recombination. This report studied the distribution of recombination sites in the genomes of 92 isolates of the potyvirus Turnip mosaic virus (TuMV); 42 came from the international gene sequence databases and an additional 50 complete genomic sequences were generated from field samples collected in Europe and Asia. The sequences were examined for evidence of recombination using seven different sequence comparison methods and the exact position of each site was confirmed by sequence composition analysis. Recombination sites were found throughout the genomes, except in the small 6K1 protein gene, and only 24 of the genomes (26%) showed no evidence of recombination. Statistically significant clusters of recombination sites were found in the P1 gene and in the CI/6K2/VPg gene region. Most recombination sites were bordered by an upstream (5') region of GC-rich and downstream (3') region of AU-rich sequence of a similar length. Correlations between the presence and type of recombination site and provenance, host type and phylogenetic relationships are discussed, as is the role of recombination in TuMV evolution.

Genome, Viral↗
PubMed1996

Localization of the recombination points in a family with two DR/DP recombinations.

In a family with a maternal DR/GLO recombination, cellular DP typing showed it to be located between DR and DP. RFLP studies done during the 9th international histocompatibility workshop gave anomalous segregation patterns of DPA and DPB bands that could be interpreted as being due to a second, paternal DR/DP recombination. This assumption was confirmed later by PCR-SSO typing. A more precise mapping has been done by new markers showing the maternal recombination to be within the TAP2 locus and the paternal recombination to be between DQB1 and DQB3. This supports earlier suggestions of a hot spot of recombination in the TAP region. The recombinations involve parental haplotypes that presently show DR/DP linkage disequilibrium in the French population and it is proposed that DR/DP recombinations occur randomly while B/DR recombinations preferentially occur on haplotypes without strong linkage disequilibrium. Existing DR/DP linkage disequilibria in a given population will thus be broken down with time. The mixed lymphocyte culture response towards an isolated DP difference was tested in this and another DR/DP recombinant family. It showed that an alloresponse towards DP may be highly variable and this suggests that it might be important to define the rules for the strength of this reaction and the possible implications for allotransplantation.

Female↗
PubMed1998

Isolation of recombinant phage clones expressing mycobacterial T cell antigens by screening a recombinant DNA library with human CD4+ Th1 clones.

A lambda gt11 recombinant DNA library of Mycobacterium leprae was screened to isolate recombinant phage clones expressing mycobacterial antigens important for T cell reactivity. The library was plated on a lawn of Escherichia coli Y1090 and recombinant antigens were expressed from isolated phage clones in 96-well plates. Pools of recombinant antigens from 12 wells were tested in T cell proliferation assays with MHC class II restricted human CD4+ Th1 clones secreting interferon-gamma and cytotoxic for antigen pulsed antigen presenting cells. By screening 1750 pools of recombinant antigens with a mixture of eight Th1 clones, we identified two recombinant phage clones that expressed recombinant mycobacterial antigens stimulatory for T cells. MHC restriction analysis and reactivity to a battery of mycobacterial antigens suggested that the two responding Th1 clones recognized mycobacterial antigens/epitopes with different MHC class II (HLA-DR) restriction requirements. Our results suggest that the methodology described in this paper is suited to isolate recombinant phage clones expressing mycobacterial recombinant antigens stimulatory for T cells of protective phenotype. Such antigens may be useful in designing new vaccines and diagnostic reagents against mycobacterial diseases.

Antigen-Presenting Cells↗
PubMed1977

[Recombination in amber mutants of bacteriophage T4B. III. Influence of X-mutation on intragenic recombination in T4 phages].

Study was made of the influence of X-mutation on interallelic and intergenic recombination at the region of genes 34-38 of phage T4B. In the case of intergenic crosses in all studied recombinations of genes mutation X caused a 2-fold decrease in recombination frequency. X-mutation showed the same effect on integenic recombination in genes 36 and 38. In the case of crossing flank markers of gene 35 the frequency of recombination decreased 3.5-fold, that of gene 34--6 fold. Crosses of double am-X mutants mapped at different sites of gene 34 allowed to detect the gradient of the effect X-mutation on recombination in gene 34 in the direction from gene 33 to gene 35. The data obtained indicate a local anomaly of DNA structure of the region of genes 34 and 35 and allowed to draw a conclusion that the degree of suppressing recombination process under the influence of X-mutation depends nor on the original recombination frequency between markers to be crossed, that is on the internal structure of the given region of the genome of bacteriophage T4. Possible reasons for specific effect of X-mutations on the recombination in genes 34 and 35 of phage T4B are discussed.

Alleles↗