Therapeutic potentialities of EWS-Fli-1 mRNA-targeted vectorized antisense oligonucleotides

We have used structured antisense oligonucleotides (AON), which are protected against extra and intracellular degradation by their internal structure. We have shown that if correctly designed this structure does not prevent them from hybridizing to the mRNA target. This concept allows reducing the number of thioate groups in the oligonucleotide and therefore the potential toxicity. Junction oncogenes are found in cancers such as certain leukemias, Ewing sarcoma, and thyroid papillary carcinomas. Ewing sarcoma is a cancer of children and young adults with bone metastasis. It is caused by a chromosomic translocation t(11;22) (q24;q12) creating a fusion gene between the genes EWS and Fli-1 giving rise to a chimeric protein which is an unnatural transcription factor. Immortalized NIH/3T3 cells transfected by the EWS-Fli-1 cDNA under the control of the LTR retroviral promoter--which do not undergo apoptosis and which became tumoral--were used for this study. As a model of Ewing sarcoma in nude mice, we have used permanently expressing human EWS-Fli-1 cells grafted to nude mice. The nanospheres or nanocapsules have been used to deliver two different AON: a phosphorothioate, and a structured chimeric AON, both targeted toward the junction area of EWS-Fli-1. Both types of AON-loaded nanoparticles inhibited the growth of the xenografted tumor after intratumoral injections into nude mice, whereas similar nanoparticles with control oligonucleotides had no effect. With AON in nanospheres, we have shown after 24 hours that the mRNA of EWS-Fli-1 was specifically down-regulated, confirming the antisense activity of the targeted AON.

Covalent coupling of a PIM-1 oncogene targeted PNA with an antennapedia derived peptide

Peptide nucleic acids (PNA) are promising antisense molecule for blocking gene expression in cell culture or in vivo. Nevertheless because they are poor efficient to pass the cellular membrane, it is necessary to use a vectorisation agent to observe an inhibitory effect. We describe the coupling of the rhodamine labeled 17-mer antisense PNA to a fusogenic peptide from antenapedia via S-S linkage, the studies of the penetration of this complex into fibroblast cells and its inhibitory effect on pim1 targeted protononcogene.

EWS fli-1 antisense nanocapsules inhibits ewing sarcoma-related tumor in mice

EWS Fli-1, a fusion gene resulting from a t(11;22) translocation is found in 90% of both Ewing's sarcoma and primitive neuroectodermal tumor (PNET). In the present study, we show that recently developed polyisobutylcyanoacrylate nanocapsules with an aqueous core were able to encapsulate efficiently high amounts of phosphorothioate oligonucleotides (ODN) directed against EWS Fli-1 chimeric RNA. Release of these ODN in serum medium was shown to be biphasic which was explained by the presence of two types of nanocapsules able to release ODN with different kinetics. In addition, nanocapsules were found to provide protection of these oligonucleotides from the degradation in serum. These ODN nanocapsules permitted to obtain inhibition of Ewing sarcoma-related tumor in mice after intratumoral injection of a cumulative dose as low as 14.4 nanomoles. This new type of non viral vector shows great potential for in vivo administration of oligonucleotides.

Modified alkaline elution allows the measurement of intact apurinic sites in mammalian genomic DNA

The presence of apurinic/apyrimidinic (AP) sites in cell genomes is known to be toxic and mutagenic. These lesions are therefore repaired in cells by efficient enzymatic systems. However, a report (Nakamura and Swenberg, Cancer Res. 59 (1999) 2522-2526) indicates an unexpected high rate of endogenous apurinic/apyrimidinic (AP) sites in genomic DNA in mammalian tissues. The technology used does not allow the authors to distinguish between intact AP sites and 3'cleaved AP sites. The corresponding values range between 2 and 4 sites per million of nucleotides in various human and rat tissues. Using a modified alkaline elution method we show here that the stationary level of intact AP sites is about 0.16 per million of nucleotides in leukemic mouse L1210 cells.

Targeting of single-stranded DNA and RNA containing adjacent pyrimidine and purine tracts by triple helix formation with circular and clamp oligonucleotides

The aim of this work was to construct an anti-messenger targeted to the pim-1 oncogene transcript, based on circular or clamp oligodeoxyribonucleotides. The formation of bimolecular triplexes by clamp or circular oligonucleotides was investigated using single-stranded targets of both DNA (5'-CCCTCCTTTGAAGAA-3') and RNA type (5'-CCCUCCUUUGAAGAA-3'). The third, 'Hoogsteen' strand of the triplex was represented by G,T-rich sequences. The secondary structures of the complexes were determined by thermal denaturation, circular dichroism and gel mobility shift experiments and shown to depend on the nature of the target strand. With DNA as target, the sequence of a clamp (or circular) oligonucleotide that formed the triple helix was 3'-GGGAGGAAACTTCTTTT-TTGTTGTTT-TT-GGTGGG-5', where the first TT dinucleotide (in italics) is a linker and the second TT (bold) represents the bridge through which the 'Hoogsteen' strand switches from one strand of the Watson-Crick duplex to the other, once the duplex is formed by the corresponding portion of the anti-messenger (underlined). The portion of the 'Hoogsteen' sequence of the triplex between the two TT dinucleotides binds to the 3' extremity of the target strand and runs parallel to it. The portion situated at the 5' end of the oligonucleotide switches to the purine tract of the complementary strand of the duplex and is antiparallel to it. In contrast, with RNA as target, for a branched clamp oligonucleotide that formed a triple helix over its entire length (5'-TTCTTCAAAGGAGGG-3' 3'-GGGTGGTTT-T-GTTGTT-5') the portion of the 'Hoogsteen' sequence that bound to the 3' extremity of the target strand had to be antiparallel to it.

Physicians' practices and opinions regarding prenatal screening for human immunodeficiency virus and other sexually transmitted diseases

BACKGROUND AND OBJECTIVES

Early prenatal diagnosis of sexually transmitted diseases (STDs), particularly human immunodeficiency virus (HIV), is critical for maternal and infant health. We conducted a survey to assess physicians' prenatal STD screening practices and opinions.

STUDY DESIGN

A random sample of obstetricians and family physicians was selected from the Minnesota Medical Association directory to complete a standardized telephone survey.

RESULTS

Eighty-three (86%) of 96 eligible obstetricians and 94 (95%) of 99 eligible family physicians completed the survey. Nearly all physicians recommend universal prenatal screening for syphilis (97%) and hepatitis B (99%); fewer physicians recommend prenatal screening for HIV (43%), chlamydia (26%), and gonorrhea (24%). Adjusting for physicians' specialty, female physicians were more likely than male physicians to recommend universal prenatal HIV screening (odds ratio [OR] = 2.1; 95% confidence interval [CI] = 1.1-4.2). Adjusting for physicians' ages, physicians with more than 20% uninsured/Medical Assistance patients were more likely than other physicians to recommend prenatal gonorrhea screening (OR = 3.1; 95% CI = 1.4-6.8); similar factors were associated with chlamydia screening. Although 89% of physicians supported universal prenatal HIV counseling and voluntary screening, the median percentage of prenatal patients screened for HIV was only 10%.

CONCLUSIONS

Most physicians reported routinely screening prenatal patients for syphilis and hepatitis B. Although many physicians agreed with recommendations for universal prenatal HIV screening, their reported screening practices varied considerably from this approach.

Automatic garage door openers: hazard for children

OBJECTIVES

Despite significant advances in automatic garage door opener design, automatic garage door openers continue to severely injure or kill children. In this investigation, we sought to determine the frequency and circumstances of accidents that have caused severe injury or death to children. We also tried to develop a means by which homeowners can evaluate their door openers.

METHODS

We present the histories of three children severely injured or killed by automatic garage door openers. We reviewed national data of similar accidents primarily published by the US Product Safety Commission and Underwriters Laboratories. Also, we evaluated 50 automatic door openers for safety of operation. The reversing mechanisms of door openers were tested using a cardiopulmonary resuscitation mannequin, a roll of paper towels, and a block of wood.

RESULTS

In the United States, at least 85 children have had permanent brain injury or have died since 1974 as a result of accidents involving automatic door openers. A review of circumstances of the accidents illustrates that accidents are caused both by use of the openers by children and by faults in design. Most accidents have occurred when children have found access to the activation devices and have been entrapped under closing doors that failed to reverse. However, in one case, an adult activated the opener and left the premises before the door completely closed. Our evaluation of 50 garage door openers showed that although 88% percent reversed when encountering a block of wood, 40% failed to reverse when coming down on a supine, child-sized cardiopulmonary resuscitation mannequin.

CONCLUSIONS

Automatic garage door openers pose a serious risk of severe injury or death to children. It is probable that many doors would not reverse if they came down on a young child. Therefore, we have devised a way for homeowners to test their door openers that closely mimics our evaluations using the mannequin by using a large roll of paper towels. If the door fails to reverse using this test, we suggest that homeowners disconnect their openers and operate the doors manually until the openers are serviced or replace their automatic openers with one that meets the latest Underwriters Laboratory standards. We also have other recommendations regarding the safe operation of the doors, including improving the safety standards for openers in apartment complexes. Compliance with these recommendations should reduce the number of injuries to children caused by garage door openers.

Investigation of the intracellular stability and formation of a triple helix formed with a short purine oligonucleotide targeted to the murine c-pim-1 proto-oncogene promotor

In our previous work we have shown that the oligonucleotide 5'-GGGGAGGGGGAGG-3' gives a very stable and specific triplex with the promoter of the murine c-pim-1 proto-oncogene in vitro[Svinarchuk, F., Bertrand, J.-R. and Malvy, C.(1994)Nucleic Acids Res., 22, 3742-3747]. In the present work, we have tested triplex formation with some derivatives of this oligonucleotide which are designed to be degradation-resistant inside the cells, and we show that phosphorothioate and the oligonucleotide with a 3' terminal amino group are still able to form triplexes. Moreover these oligonucleotides, like the 13mer oligonucleotide of similar composition [Svinarchuk, F., Paoletti, J., and Malvy, C. (1995) J. Biol. Chem., 270, 14068-14071], are able to stabilize the targeted duplex. In vivo DMS footprint analysis after electroporation of the pre-formed triplex into the cell have shown the presence of the triple helix inside the cells. This triplex structure partially blocks c-pim-1 promotor activity as shown by transient assay with a c-pim-1 promoter-luciferase gene construct. To our knowledge these data are the first direct evidence that conditions inside cells are favorable for triplex stability with non-modified oligonucleotides. However we were unable to show triplex formation inside living cells using various methods of oligonucleotide delivery. We suppose that this may be due to the oligonucleotide being sequestered by cellular processes or proteins. Further work is needed to find oligonucleotide derivatives and ways of their delivery to overcome the problem of triplex formation inside the cells.

In vitro inhibition of the pim-1 protooncogene by chimeric oligodeoxyribonucleotides composed of alpha- and beta-anomeric fragments

We show that oligodeoxyribonucleotides (oligos) composed of alpha- and beta-anomeric sections can be used as antisense compounds. An octamer has been chosen as an effector domain to form a substrate for RNaseH. This octamer is complementary to the translation start site of the pim-1 protooncogene mRNA. Chimeric alpha-beta oligos and their beta-analogs have a similar binding affinity for their target. These oligos also direct efficient RNaseH-mediated cleavage of target mRNA. Among all alpha-beta oligos studied, one with an alpha-fragment bound by its 3'-end to the 3'-end of the beta-octamer is the most resistant to nucleolytic digestion in biological media. The alpha-beta oligos have been found to inhibit in vitro translation of pim-1 RNA with specificity.

A short purine oligonucleotide forms a highly stable triple helix with the promoter of the murine c-pim-1 proto-oncogene

A homopurine-homopyrimidine region of murine c-pim-1 proto-oncogene was chosen as a target for triple-helix-forming oligonucleotide. Oligonucleotide 5'-GGG-GAGGGGGAGG-3' was shown to bind to its target sequence in the presence of 50 mM Na+ or K+, 10 mM MgCl2 and 20 mM Tris-acetate, pH 7.5. This oligonucleotide is bound in an antiparallel orientation with respect to the homopurine sequence. As was shown by co-migration assay the triplex is stable up to 65 degrees C. At 37 degrees C it was practically irreversible: after 24 hours of co-migration assay there was no traces of triplex dissociation. The rate of triplex formation was highly accelerated with increase of temperature and Mg2+ concentration. This rate was higher for superhelical DNA when compared to the linear and circular ones and the preference was dependent from temperature and Mg2+ concentration. The precision of this interaction is extremely high: sequences in c-pim-1 promoter region with only one substitution when compared to the target gave negligible triplex formation under investigated conditions. These data suppose that natural triplex structures could play an important role in eukaryotic gene regulation and/or chromatin structure formation.

Sequence-specific interaction of alpha-beta-anomeric double-stranded DNA with the p50 subunit of NF kappa B: application to the decoy approach

The potential use of alpha-beta-anomeric duplex oligonucleotides to inhibit transcription factor activity by the decoy approach is investigated in this report. Indeed, several alpha-beta-anomeric heteroduplexes display a sequence-specific interaction with the p50 subunit of the transcription factor NF kappa B. Used in a decoy approach, these duplexes interact strongly enough with this transcription factor to modulate the expression of a reporter gene, under the control of NF kappa B. However, all the alpha-beta-anomeric heteroduplexes do not interact with the p50 subunit; the sequence of the chirally natural beta-anomeric strand may explain the different recognition properties of the protein. The analysis of the appropriate beta-anomeric sequences is consistent with a preferential interaction of the p50 subunit with one strand of double-stranded DNA.

Alpha beta chimeric antisense oligonucleotides: synthesis and nuclease resistance in biological media

A new type of chimeric oligonucleotides composed of alpha- and beta-sections is described. The sequence of eight beta-nucleotides flanked at 3'- or/and 5'-ends by nuclease-resistant alpha-oligonucleotides has been chosen as an effector domain to form a substrate for RNase H. The synthesized oligonucleotides are complementary to the translation initiation site of the pim protooncogene mRNA. We used the chemical ligation method to prepare the chimeric oligonucleotides. The thermal stability of heteroduplexes formed by the alpha beta oligonucleotides with a complementary strand is not significantly altered compared to that of their beta-analogs. These oligonucleotides promote efficient RNase H-mediated cleavage of pim mRNA. Among the alpha beta oligonucleotides studied, one with an alpha-fragment bound by its 3'-end to the 3'-end of the beta-octanucleotide proved to be the most resistant to nucleolytic digestion in human plasma, calf serum, and murine fibroblast lysate. This alpha beta oligonucleotide directs more specific RNA cleavage by RNase H than its beta beta counterpart.

9-Aminoellipticine-derivatized alpha- and beta-oligodeoxyribonucleotides targeted to the cap of beta-globin mRNA: hybridization to natural and engineered mRNA, inhibition of translation, and improved effect of tandem chains

We studied the duplex stability and the antimessenger activity of 9-aminoellipticine-5'-functionalized alpha- and beta-anomeric DNA sequences complementary to the first 14 nucleotides of the rabbit beta-globin mRNA. The duplex formed by the beta-conjugate with the natural mRNA target possessed a marginally better stability to that of the duplex formed by the unfunctionalized compound, as measured by the thermal elution. The alpha-conjugate did not anneal to native mRNA, possibly due to the interference of the 9-aminoellipticine with the cap structure and, unlike the beta-adduct, was practically inactive as inhibitor of translation in a cell-free system. However, it did hybridize to an RNA construction containing the beta-globin mRNA plus an additional 50 bases in 5'. Surprisingly, translation from this construction was inhibited by the alpha-species in spite of the nonvicinity of the target to the cap. Both alpha and beta conjugates hybridized to a DNA 14-mer of the same sequence as that targeted onto the mRNA. Thermal denaturation and fluorescence spectroscopy showed that the drug brought no considerable stabilization to the duplex, the linker presumably being unfavorable to intercalation. An increased stability of the complex and a higher inhibitory effect on cell-free beta-globin translation were obtained with two contiguous beta-oligomers of which one was functionalized.

Molecular modelling of 9-aminoellipticine interactions with abasic oligonucleotides

We have used molecular mechanics to study the insertion of the DNA intercalating agent 9-aminoellipticine (9AE) into single and double stranded abasic oligonucleotides containing abasic sites in the aldose or furanose conformations. 9AE-abasic oligonucleotide complexes have been considered with 9AE bound at abasic sites as a covalent complex, a reversible complex or a Schiff base. Results are in good agreement with experimental data available on abasic oligonucleotides (melting temperature measurement, NMR results) and allow an analysis of different possible structures for 9AE-abasic oligonucleotide complexes. Hypotheses concerning the role of 9AE-abasic site complexes in enzymatic inhibition are formulated from these data.

9-amino-ellipticine inhibits the apurinic site-dependent base excision-repair pathway

The aromatic amine 9-amino-ellipticine is a synthetic DNA intercalating compound derived from the antitumor agent ellipticine, which cleaves at very low doses DNA containing apurinic sites by beta-elimination through formation of a Schiff base. This compound has been shown to potentiate the cytotoxic effect of alkylating drugs, such as dimethyl sulfate, in E. coli through a mechanism involving apurinic sites. We have studied the ability of 9-amino-ellipticine to inhibit an enzymatic repair system mimicking base-excision repair, in which E. coli exonuclease III only presents an endonuclease for apurinic/apyrimidinic site activity. 10 microM of 9-amino-ellipticine inhibits 70% of apurinic site repair. Other intercalating agents with similar affinities for DNA do not induce any inhibition. In another system designed for the direct assay of the exonuclease III-induced incisions 5' to AP sites 10 microM of 9-amino-ellipticine inhibits 65% of the endonuclease for apurinic/apyrimidinic site activity of E. coli exonuclease III. The 9-amino-ellipticine-induced formation of a 2',3'-unsaturated deoxyribose and cleavage at the 3' side of the apurinic site, and possible creation of an adduct, as suggested by Bertrand and coworkers (1989), on the 3' position of the deoxyribose seem to strongly inhibit the endonuclease for apurinic/apyrimidinic site activity. 9-Amino-ellipticine appears therefore to be the first small ligand which can inhibit, by an irreversible modification of the substrate, the repair of apurinic sites through the base excision-repair pathway at a pharmacological concentration.

Structural features associated with alpha- anomeric in oligo-alpha-thymidylates

Comparison between gel electrophoresis migrations of oligo-alpha-thymidylates and oligo-beta-thymidylates indicates that the migration of alpha-oligonucleotides under native conditions is different from the migration of beta-oligonucleotides when the number of thymines, part of the sequence, is higher than 5. Such difference disappears when the gels are run under denaturing conditions. This, together with UV spectra, indicates that the structure of alpha-oligonucleotides is more organized than the structure of beta-oligonucleotides and that such an organisation appears for a length higher than 5 monomeric units.

Synthesis, thermal stability and reactivity towards 9-aminoellipticine of double-stranded oligonucleotides containing a true abasic site

A 13 mers abasic oligonucleotide was synthetized. It was therefore possible to compare thermal stability and reactivity of duplex oligonucleotides either with an apurinic/apyrimidinic site or without any lesion. An important decrease in the melting temperature appeared for duplexes with an abasic site. The chemical reaction of these modified oligonucleotides with the intercalating agent 9-aminoellipticine was studied by gel electrophoresis and by fluorescence. The formation of a Schiff base between 9-aminoellipticine and abasic sites was rapid and complete with duplexes at 11 degrees C. Schiff base related fluorescence and beta-elimination cleavage were more important with the apyrimidinic sites than with the apurinic ones. When compared to previous results obtained with the model d(TprpT) some unexpected behaviours appeared with longer and duplex oligonucleotides. For instance only partial beta-elimination cleavage was observed. It is likely that stacking parameters in the double helix play a great role in the studied reaction.

Comparative activity of alpha- and beta-anomeric oligonucleotides on rabbit beta globin synthesis: inhibitory effect of cap targeted alpha-oligonucleotides

Alpha-anomeric oligonucleotides are resistant to nucleases and display parallel annealing to RNA complementary sequences. We compared the effect of alpha- and beta-oligonucleotides targeted against various mRNA regions on the rabbit beta globin in vitro synthesis. In order to determine the role of RNase H, experiments were performed in both rabbit reticulocyte lysate and wheat germ extract. As expected beta-oligonucleotides were found more efficient in wheat germ extract which is rich in RNase H activity and alpha-oligonucleotide targeted against the initiation codon or downstream had no effect because they do not induce mRNA cleavage by RNase H. However, we report, for the first time, a specific translation inhibition by alpha-oligonucleotides. This occurs provided they are targeted against the cap region in 5' of the mRNA.

Mechanism of cleavage of apurinic sites by 9-aminoellipticine

We have studied the kinetics of breakage of apurinic (AP) sites by the intercalating agent 9-aminoellipticine using fluorimetric methods with single (ss)- and double (ds)-stranded apurinic DNA. In order to understand the chemical process, high performance liquid chromatography was used to follow the reaction kinetics with the apurinic oligonucleotide model T(AP)T. The unstable intermediate, which is responsible for the beta-elimination step, is a Schiff base resulting from the interaction of the amino group of the aromatic amine with the aldehyde function of the deoxyribose moiety (AP site). Fluorescence occurs simultaneously with the breakage of both ss and ds DNA and of the oligonucleotide and arises from the formation of a conjugated double bond on the Schiff base through the beta-elimination reaction. In optimal conditions, the second order rate constant for the fluorescence build up is 15 x 10(3) min-1 M-1 for ds DNA and 0.105 x 10(3) min-1 M-1 for T(AP)T. The ability of 9-aminoellipticine to induce fluorescence and breakage of ss DNA and T(AP)T shows that intercalation is not essential for this reaction to occur. Nevertheless, the greater rate constant with DNA suggests that stacking is an important parameter for the reaction of the aromatic amine with the AP site.

Inhibition of Moloney murine leukemia virus reverse transcriptase by alpha-anomeric oligonucleotides

After parallel hybridization to complementary template RNA, alpha-anomeric oligonucleotides are not primers for Moloney murine leukemia virus reverse transcriptase. As can be expected they are competitors of classical primer oligonucleotides (beta-anomeric). They therefore inhibit the RNA dependent DNA polymerase activity of Moloney murine leukemia virus reverse transcriptase with either homopolymeric or heteropolymeric substrates. Non complementary alpha-oligonucleotides display no inhibitory activity. alpha-Oligonucleotides are therefore potential candidates for inhibition of retroviral reverse transcriptases by interference with the primer binding sites.

Alpha-anomeric DNA: beta-RNA hybrids as new synthetic inhibitors of Escherichia coli RNase H, Drosophila embryo RNase H and M-MLV reverse transcriptase

Nuclease-resistant alpha-anomeric DNA:beta-RNA hybrids are inhibitors of Escherichia coli RNase H, and Drosophila embryo RNase H. RNase H activities were measured by polyacrylamide gel electrophoresis, employing a short substrate, (A)12:d[G-G-(T)12-G-G], or by acid-solubility techniques, using a long substrate, poly(A):poly(dT). Strand exchanges which could be responsible for the observed inhibition have been ruled out by S1 nuclease experiments and by using inhibitors which do not allow strand exchange. Our results suggest that RNase H, for which DNA:RNA duplexes are the natural substrates, binds to non-physiological alpha-DNA:RNA hybrids and is consequently inhibited. These hybrids also inhibit the RNA-dependent DNA polymerase activity of M-MLV reverse transcriptase, therefore appearing as potential inhibitors of at least two reverse transcriptase activities. However, the inhibitory effect of these hybrids with respect to M-MLV reverse transcriptase is also observed with the single-stranded alpha-DNA itself. Unexpectedly, polymerase activity is highly stimulated by alpha-oligos, analogous in their sequence to the beta primer used at a concentration unable to generate a detectable synthesis. These results suggest that the inhibition of reverse transcriptase activity with the alpha:beta may occur at different levels.

Alpha are more stable than beta anomer oligonucleotides in 3T3 cellular extracts

We have compared the stability of alpha and beta anomeric oligonucleotides in NIH 3T3 cellular extracts. We had already shown that alpha are much more resistant than beta oligonucleotides towards purified nucleases. This result is confirmed when using cellular extracts although the difference is smaller. When alpha molecules are combined with an intercalating agent binding in the 3' position a synergistic increase of resistance to degradation is observed.

Involvement of apurinic sites in the synergistic action of alkylating and intercalating drugs in Escherichia coli

The toxicity of the intercalating compounds 9-aminoellipticine (9AE) and isopropyl-oxazolopyridocarbazole (Ipr-OPC) were studied. The inhibitory effect of non-toxic doses of 9AE, which incises DNA at apurinic (AP) sites, or Ipr-OPC, which does not cleave DNA at AP sites, with non-toxic doses of the alkylating agent dimethylsulphate (DMS) on the growth of Escherichia coli strain AB1157, is additive. The same result has been observed with an exonuclease III mutant which has only 10% of the AP endonuclease activity. However, 9AE or Ipr-OPC display a synergistic toxic effect with a DMS concentration which allows 20% of E. coli AB1157 survival. This synergy is increased for 9AE in the AP endonuclease mutant when compared to the wild-type strain. Under identical conditions 9AE and Ipr-OPC have no synergistic effect on a mutant deficient in the enzymes which generate AP sites. Therefore AP sites are involved in the synergistic toxicity of DMS and the studied intercalating agents. However, the precise role of the interaction of intercalating agents with AP sites, either without cleavage (type 1 compounds) or with cleavage (type 2 compounds), in the observed effect remains an open question.

alpha-DNA. VI: Comparative study of alpha- and beta-anomeric oligodeoxyribonucleotides in hybridization to mRNA and in cell free translation inhibition

alpha and beta-anomeric d(G2T12G2) oligodeoxyribonucleotides were compared for their hybridization to rA12: the observed melting temperatures are 27 degrees C for beta-oligodeoxyribonucleotide/RNA hybrid and 53 degrees C for alpha-oligodeoxyribonucleotide/RNA. alpha-oligonucleotides with the four bases, complementary to natural mRNAs, were synthesized for the first time, labeled at their 5'-end with [32P] and used as probes in Northern blot experiments. In spite of these higher affinities for their target RNA's, they were unable to block translation of natural or synthetic mRNA's in rabbit reticulocyte lysate. We have studied the RNase H activity on model rA12:alpha- or beta-d(G2T12G2) hybrids or on mRNA:alpha- or beta-oligonucleotides hybrids. Specific hybridization protects RNA strech when using alpha-oligonucleotides but not beta-oligonucleotides. Thus, our results show the inability of RNase H to degrade RNA in alpha-oligodeoxyribonucleotides:RNA duplexes.

alpha-DNA II. Synthesis of unnatural alpha-anomeric oligodeoxyribonucleotides containing the four usual bases and study of their substrate activities for nucleases

This paper describes for the first time the synthesis of alpha-oligonucleotides containing the four usual bases. Two unnatural hexadeoxyribonucleotides: alpha-[d(CpApTpGpCpG)] and alpha-[d(CpGpCpApTpG)], consisting only of alpha-anomeric nucleotide units, were obtained by an improved phosphotriester method, in solution. Starting material was the four base-protected alpha-deoxyribonucleosides 3a-d. Pyrimidine alpha-deoxynucleosides 3a and 3b were prepared by self-anomerization reactions followed by selective deprotection of sugar hydroxyles, while the two purine alpha-deoxynucleosides 3c and 3d were prepared by glycosylation reactions. In the case of guanine alpha-nucleoside derivative a supplementary base-protecting group: N,N-diphenylcarbamoyl was introduced on O6-position in order to avoid side-reactions during oligonucleotide assembling. The hexadeoxynucleotide alpha-[d(CpApTpGpCpG)] was tested as substrate of selected endo- and exonucleases. In conditions where the natural corresponding beta-hexamer was completely degradated by nuclease S1 and calf spleen phosphodiesterase, the alpha-oligonucleotide remained almost intact.

Quantification by fluorescence of apurinic sites in DNA

Time dependent fluorescence is observed when single or double stranded DNA with apurinic sites are mixed with 9-NH2-ellipticine. A concentration dependent plateau is obtained which is linearly related to the ratio of apurinic sites in DNA. We therefore suggest that it is possible to have a direct measurement of apurinic sites in DNA by fluorescence.

Differential reactivity of 9-NH2-ellipticine on apurinic and apyrimidinic sites in circular DNA

Endonucleases for apurinic sites as well as chemical compounds reacting with aldehydes do not generally differentiate between apurinic and apyrimidinic sites. We have studied the effect of the apurinic site reagent, 9-NH2-ellipticine, on apyrimidinic sites enzymatically generated on PBR322 DNA and compared it to its' action on apurinic PM2 and PBR322 DNAs. In conditions where this compound induces breakage of apurinic sites, it does not display any action on apyrimidinic sites.

Ellipticines: correlation between in vitro DNA intercalation and physiological properties?

The in vitro DNA-intercalator ellipticine and five of its derivatives have been investigated for some of their physiological effects on several Escherichia coli strains. The highly water-soluble, quaternarized derivatives of ellipticine have no bactericidal effect and do not induce the synthesis of rec A protein. Ellipticine itself, as well as the derivatives obtained by adding an amino or an hydroxyl substituent in position 9, promotes the induction of rec A protein and is cytostatic on some bacterial strains. The non-intercalating brominated derivative is a strong bactericidal agent, which apparently promotes the lysis of the bacteria. At low concentrations, it slightly induces the synthesis of rec A protein. We conclude that there is no correlation at all between the physiological properties of the ellipticines and their physico-chemical behavior in vitro.

[Recent trends in Spanish emigration]

Depuis 1960, l'évolution de l'émigration permanente espagnole s'articule en deux phases. Jusqu'en 1974, elle redevient massive (100 000 émigrants par an). Elle se tourne vers l'Europe industrialisée, préférée aux nouveaux mondes, et recrute dans l'ensemble du pays, les provinces méridionales se joignant aux pôles séculaires. Les émigrants présentent alors les caractéristiques socio-démographiques classiques : jeunesse, surmasculinité, activités subalternes ou pénibles... La crise des économies industrielles a mis fin en 1974 à l'émigration vers l'Europe sans que les flux transocéaniques s'amplifient. Toutes les zones de provenance des migrants, traditionnelles ou récentes, sont affectées avec plus ou moins d'ampleur, ce qui ne saurait manquer de poser de graves problèmes d'emploi et d'équilibre de la balance des comptes dans une économie espagnole non épargnée par la crise.