Molecular analysis of ethylene oxide-induced mutations at the HPRT locus in human diploid fibroblasts

Ethylene oxide (EtO)-induced mutations in the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene were characterized in 28 independently derived 6-thioguanine-resistant human diploid fibroblast clones using polymerase chain reaction-based techniques and Southern blot analysis. Sequence analysis revealed one single base pair deletion and 13 base substitutions, nine of which were transversions: five AT-->TA, three GC-->TA and one GC-->CG. Four mutants were found to have GC-->AT transitions. Seven of the point mutations caused splicing errors. Six occurred in splice site sequences and one created a new splice acceptor site 16 bp upstream of exon 9. Three splice mutations were localized at the same site in the splice donor sequence of intron 8. Fourteen mutants had large HPRT gene deletions. In seven mutants the entire HPRT gene was deleted. The remaining deletion mutants had a truncated HPRT gene, where one or several exons were lost. These results show that EtO induces many different kinds of HPRT mutations, among which as many as 50% are large deletions.

Hprt activities and RNA phenotypes in 6-thioguanine resistant human T-lymphocytes

The phenotypic effects of mutation in the hypoxanthine phosphoribosyltransferase (hprt) gene on hprt enzyme activity and hprt mRNA levels were studied in 6-thioguanine (TG) resistant human T-cell clones with various types of hprt mutation. The mean enzyme activity in 16 TG selected clones was less than 1% of the mean in unselected clones. The hprt mRNA levels, measured by a quantitative RNA/RNA solution hybridization assay, were within the normal range in 38% of the mutant clones. Reduced hprt mRNA levels were found in all of three nonsense mutations, four out of five splicing mutations, both of two clones with genomic alterations, three out of five missense mutations and one out of four frameshift mutations caused by 1-4-bp deletions. Intermediate and high enzyme activity and normal hprt mRNA levels were found in two TG selected clones where no hprt mutation was detected. Several clones with very low hprt mRNA levels were found to yield hprt cDNA by PCR amplification. These results show that hprt mutation leads to decreased steady state levels of hprt mRNA in a majority of TG resistant T-cell clones, and that many different types of hprt mutation can have this effect.

Clonal chromosome aberrations and genomic instability in X-irradiated human T-lymphocyte cultures

To study the effects of X-irradiation on clone forming ability and karyotypic abnormalities in human peripheral blood lymphocytes, cells were exposed to 3 Gy of X-rays in vitro and either individual T-cell clones or long-term T-cell cultures were established. The karyotypes were analyzed in G-banded chromosome preparations after proliferation for 9-34 days in vitro. T-cell clonal karyotype abnormalities were found in 24 of 37 (65%) irradiated and in two of 43 (5%) control clones. Balanced reciprocal translocations and deletions were the predominating types of clonal aberrations. Complex aberrations and unstable karyotypes were found in about half of the irradiated clones. Some of the T-cell clones demonstrated sequential change from normal to aberrant karyotype. Other clones seemed to develop multiple, heterogeneous chromosomal aberrations during growth in vitro. X-Irradiated T-cells grown in long-term T-cell culture displayed karyotype abnormalities in 60-80% of the cells, and the types of aberrations were similar to those found in the individual, irradiated T-cell clones. An increasing number of cells with the same abnormal karyotype was observed when the cultivation time was extended, indicating clonal proliferation. These results demonstrate that a surprisingly high proportion of T-cells with stable and often complex irradiation-induced chromosome aberrations are able to proliferate and form expanding cell clones in vitro. Furthermore, the results indicate that X-irradiation induces latent chromosome damage and genomic instability in human T-lymphocytes.

Duplication in the hypoxanthine phosphoribosyl-transferase gene caused by Alu-Alu recombination in a patient with Lesch Nyhan syndrome

We have determined the structure, at the nucleotide sequence level, of a duplication in the hprt gene in a patient with Lesch-Nyhan syndrome (LN). The duplication extends over exons 7 and 8 and approximately 1.8 kb of the surrounding hprt sequence. The duplication junction is localized within two Alu sequences and has apparently been generated by unequal homologous recombination. This is the second reported case of a partial duplication of the hprt gene in an LN patient, and the first that involves an Alu-Alu recombination.

Missense mutations and evolutionary conserved amino acids at the human hypoxanthine phosphoribosyl-transferase locus

Molecular characterization of in vivo mutation at the human hypoxanthine phosphoribosyltransferase (hprt) locus has revealed a broad spectrum of mutation, both with regard to germ-line mutation in Lesch-Nyhan and gout patients, and somatic mutation in 6-thioguanine resistant T-lymphocytes from healthy individuals. The pattern of missense mutation shows a non-random distribution with a preferential location to codons for amino acids which are identical in human and the two parasites Schistosoma mansoni and Plasmodium falciparum. Although these 'evolutionary conserved' amino acids account for only 32% of the amino acids in the human hprt protein, they are involved in 76% of the missense mutations at the hprt locus in human T-lymphocytes, 67% in Lesch-Nyhan patients (with severe hprt-deficiency), but only 43% in gout patients (with partial hprt deficiency). This observation supports the notion that evolutionary conserved amino acids constitute functionally important sites in the hprt enzyme, and missense mutations affecting these amino acids will often lead to complete loss of enzyme activity. Substitutions of 'non-conserved' amino acids cause less severe hprt-deficiency (as seen in the gout patients), or may even escape clinical diagnosis. These considerations are important for the understanding of structure-activity relationships in the hprt protein, possible differences between hprt mutational spectra in germ-line and somatic cells, and the mutational spectra induced by specific exogeneous mutagens.

Strand specificity for mutations induced by (+)-anti BPDE in the hprt gene in human T-lymphocytes

Mutations in the hprt gene in T-lymphocyte clones isolated from primary cultures treated with the (+)-anti enantiomer of 7,8-dihydroxy-9,10-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (BPDE) in vitro, and from untreated control cultures, were characterized using polymerase chain reaction and direct sequencing of hprt cDNA and genomic fragments. The spectrum of BPDE-induced mutations was very specific and clearly different from the background spectrum, which comprised many different types of mutations. Of the BPDE-induced mutations, 20/22 were transversions of GC base pairs and 18/22 were GC greater than TA transversions, which is in agreement with what has been found in other mammalian systems. While no particular 'hotspot' was observed for BPDE in the hprt gene, a sequence context specificity was detected. Ten of the 14 BPDE-induced mutations in the coding region were located in the sequence context AGG, and 2 in AG dinucleotides, which indicates that such sequences are sensitive to BPDE mutagenesis. Nine of the 22 BPDE-induced mutations and 2/12 background point mutations caused mRNA splicing errors. Six of the BPDE-induced splicing errors were caused by GC greater than TA transversions in the AG dinucleotide of different splice acceptor sites, which indicates that these sites may be frequent targets of BPDE mutagenesis. All mutated GC base pairs in the BPDE-induced spectrum were oriented so that the guanine was located on the non-transcribed strand. Assuming that the premutagenic lesion in these cases was covalent binding of BPDE to guanine and that BPDE bound randomly to both strands, the strand specificity of the BPDE-induced mutations indicates that preferential excision repair of BPDE adducts on the transcribed strand occurs in the hprt gene in human T-cells.

Novel Bacillus thuringiensis insecticidal crystal protein with a silent activity against coleopteran larvae

A novel Bacillus thuringiensis crystal protein with a silent activity against the Colorado potato beetle is described. The crystal proteins are produced as bipyramidal crystals. These crystals contain a protein of 129 kDa with a trypsin-resistant core fragment of 72 kDa. Neither a spore-crystal mixture nor in vitro-solubilized crystals are toxic to any of several Lepidoptera and Coleoptera species tested. In contrast, a trypsin-treated solution containing the 72-kDa tryptic core fragment of the protoxin is highly toxic to Colorado potato beetle larvae. The crystal protein-encoding gene was cloned and sequenced. The inferred amino acid sequence of the putative toxic fragment has 37, 32, and 33% homology to the CryIIIA, CryIIIB, and CryIIID toxins, respectively. Interestingly, the 501 C-terminal amino acids show 41 to 48% amino acid identity with corresponding C-terminal amino acid sequences of other crystal proteins. Because of the toxicity of the fragment to the Colorado potato beetle and because of the distinct similarities of the toxic fragment with the other CryIII proteins, this gene was given a new subclass name (cryIIIC) within the CryIII class of coleopteran-active crystal proteins. CryIIIC represents the first example of a crystal protein with a silent activity towards coleopteran insect larvae. Natural CryIIIC crystals are not toxic. Toxicity is revealed only after an in vitro solubilization and activation step.

Mutation analysis and prenatal diagnosis in a Lesch-Nyhan family showing non-random X-inactivation interfering with carrier detection tests

A nonsense mutation at the CpG-site in the codon for Arg(169) in the gene for hypoxanthine phosphoribosyltransferase (hprt) was identified by genomic polymerase chain reaction (PCR) and DNA sequencing in cultured fibroblasts from two brothers with Lesch Nyhan's syndrome. The recurrence of mutation at this CpG-site in several unrelated Lesch-Nyhan families suggests that deamination of 5-methylcytosine is a possible mechanism for mutagenesis. The level of hprt-mRNA in the fibroblasts of the patients was similar to that in healthy controls, whereas hprt-enzyme activity was not detectable. The mutation in this family was also identified in five female relatives and prenatally in a male fetus. Unexpectedly, results from hair follicle analyses and fibroblast selection studies in 8-azaguanine and 6-thioguanine medium showed a non-carrier phenotype in three of the female heterozygotes, whereas X-inactivation mosaicism was demonstrated in one heterozygote. A possible explanation for the apparent non-random X-inactivation in this family is the co-existence of the hprt mutation with an undefined X-linked lethal mutation. This observation is of practical relevance for carrier detection in other Lesch-Nyhan families.

Autocrine biological effects of glycosyl inositol phosphate produced by reconstituted pig thyroid follicles: role of pertussis toxin sensitive G proteins

We examine the autocrine activity of glycosyl inositol phosphate (InP-gly) on thyroid metabolism. The cAMP accumulation promoted by thyrotropin (TSH) or forskolin was modulated by InP-gly, stimulated by the lowest tested concentration (10(-8) M) and progressively inhibited by higher concentrations. Iodide uptake and iodine organification were decreased in a concentration-dependent manner by InP-gly alone, or in the presence of TSH. The IAP component of pertussis toxin blocked the inhibitory action of InP-gly on cAMP accumulation by reconstituted thyroid follicles (RTF), suggesting the participation of Gi protein. But the same treatment with IAP was without effect on iodine metabolism, suggesting that there is a second target for InP-gly, more distal than Gi protein, or coupled to another G protein which is insensitive to the toxin.

Visual dysfunction without retinitis in patients with acquired immunodeficiency syndrome

Patients with human immunodeficiency virus infection may have noninfectious and infectious retinopathies, as well as clinical symptoms consistent with optic nerve dysfunction. Noninfectious acquired immunodeficiency syndrome-related retinopathy is seen in most patients with AIDS. Morphologic studies have shown that the number of retrobulbar optic nerve fibers in patients with AIDS is decreased compared to the number of optic nerve fibers in normal control eyes. To determine whether these patients had a visual dysfunction consistent with damage to the macula and optic nerve, 78 subjects (156 eyes) were studied using color-vision and contrast-sensitivity testing. The Farnsworth-Munsell 100-Hue color-vision test was performed on all subjects and age-corrected color-vision scores for all groups were compared. A significant decrease in color discrimination was found in the patients with AIDS (P less than .001). Contrast-sensitivity testing disclosed a deficit of contrast threshold in patients with AIDS at four of five spatial frequencies and in patients with AIDS-related complex at three of the five spatial frequencies examined. This study demonstrated a functional visual deficit in eyes without retinitis consistent with dysfunction of the macula or optic nerve in patients with AIDS.

Nucleotide sequence of gene cryIIID encoding a novel coleopteran-active crystal protein from strain BTI109P of Bacillus thuringiensis subsp. kurstaki

The nucleotide sequence of a novel insecticidal crystal protein(Cry)-encoding gene from a Bacillus thuringiensis serotype kurstaki isolate is described. The gene is related to the known coleopteran-active cryIII genes and encodes a CryIIID that is much more active against Colorado potato beetle than other CryIII.

The fragile X mutation does not have any major effect on the expression of the hypoxanthine phosphoribosyltransferase (HPRT) locus in human fibroblasts

The possible influence of the fragile X mutation at Xq27 on the expression of the neighbouring gene (at Xq26) for hypoxanthine phosphoribosyl transferase (HPRT) was studied by determination of the levels of HPRT-RNA and HPRT enzyme activity in fibroblast cell cultures from 7 fragile X patients. These levels were lower (although not statistically significantly lower) than in normal fibroblast cultures. Hence, these data do not support the notion of a major effect of the fragile X mutation on the expression of the HPRT gene.

The effect of glycosyl inositol-phosphate on cAMP production in isolated rat fat-cells is transduced by a pertussis toxin sensitive G-protein

In fat-cells, insulin increases synergistically the inhibitory effects of adenosine and prostaglandin E2 on adenylyl cyclase activity. When the endogenous production of these feedback inhibitors is suppressed, insulin is no more active in conditions where glycosyl inositol-phosphate which is a putative mediator of its action, is always efficient. Moreover, glycosyl inositol-phosphate signal is transduced by a G protein sensitive to IAP intoxication.

Escherichia coli Fpg protein and UvrABC endonuclease repair DNA damage induced by methylene blue plus visible light in vivo and in vitro

pBR322 plasmid DNA was treated with methylene blue plus visible light (MB-light) and tested for transformation efficiency in Escherichia coli mutants defective in either formamidopyrimidine-DNA glycosylase (Fpg protein) and/or UvrABC endonuclease. The survival of pBR322 DNA treated with MB-light was not significantly reduced when transformed into either fpg-1 or uvrA single mutants compared with that in the wild-type strain. In contrast, the survival of MB-light-treated pBR322 DNA was greatly reduced in the fpg-1 uvrA double mutant. The synergistic effect of these two mutations was not observed in transformation experiments using pBR322 DNA treated with methyl methanesulfonate, UV light at 254 nm, or ionizing radiation. In vitro experiments showed that MB-light-treated pBR322 DNA is a substrate for the Fpg protein and UvrABC endonuclease. The number of sites sensitive to cleavage by either Fpg protein or UvrABC endonuclease was 10-fold greater than the number of apurinic-apyrimidinic sites indicated as Nfo protein (endonuclease IR)-sensitive sites. Seven Fpg protein-sensitive sites per PBR322 molecule were required to produce a lethal hit when transformed into the uvrA fpg-1 mutant. These results suggest that MB-light induces DNA base modifications which are lethal and that these modifications are repaired by Fpg protein and UvrABC endonuclease in vivo and in vitro. Therefore, one of the physiological functions of Fpg protein might be to repair DNA base damage induced by photosensitizers and light.

Expression of the hypoxanthine phosphoribosyl transferase gene in resting and growth-stimulated human lymphocytes

Expression of the hypoxanthine phosphoribosyl transferase (hprt) gene was studied in resting and growth stimulated human lymphocytes by determinations of hprt-RNA and enzyme activity levels in cell extracts. Hprt-RNA was determined by quantitative solution hybridization and enzyme activity by measuring the rate of conversion of [14C]hypoxanthine to inosine 5'-monophosphate. In resting Go-lymphocytes, the hprt activity (5 nmol/h per 10(6) cells) was twice as high as in human fibroblasts, whereas the hprt-RNA level was very low (0.3 pg per 10(6) cells, or approx. one mRNA molecule per cell). Both RNA and enzyme activity remained at these levels in cells that were incubated in the presence of cycloheximide (CHX, 20 micrograms/ml) for up to 48 h, which suggests that hprt gene expression in resting lymphocytes depends mainly on a stable protein with a half-life of more than 48 h. In phytohemagglutinin (PHA) stimulated lymphocytes, the hprt-RNA levels increased 10-20-fold, while the enzyme activity increased 5-fold. The addition of hydroxyurea (0.01 M) to the culture medium did not prevent the increase of hrpt-RNA, whereas the increase of both RNA and enzyme activity was abrogated in the presence of CHX. Thus, the induction of hprt expression in growth stimulated lymphocytes requires new protein synthesis, and is not coupled to DNA replication. In long-term lymphocyte cultures, both hprt-RNA and enzyme activities showed high steady-state levels. After removal of PHA and growth factors from the culture medium the hprt-RNA levels decreased by over 80% within 24 h, while the enzyme activity was unaffected. Inhibition of transcription by actinomycin D (5 micrograms/ml) caused a rapid decay of the hprt-RNA, with an estimated half-time of 5.1 h. When CHX was added to actinomycin D inhibited cells, the rate of hprt-RNA breakdown was reduced. The hprt enzyme activity declined by approx. 50% during 24 in the presence of CHX. Thus, the enhanced expression of hprt-RNA in proliferating lymphocytes depends on continuous growth stimulation and seems to be associated with a high transcriptional activity and turnover of the RNA. In contrast, the enzyme activity is relatively stable, and less sensitive to alterations of growth conditions.

Mutations induced by benzo[a]pyrene diolepoxide at the hprt locus in human T-lymphocytes in vitro

Human T-lymphocytes have been treated with benzo[a]pyrene diolepoxide (BPDE) in vitro and T-cell clones mutated in the hprt gene have been isolated. The mutant frequencies in BPDE-treated T-cell cultures were on average 24-fold higher than those of untreated cultures. Thus, BPDE is a potent inducer of gene mutation in this system. In order to examine which types of mutations are induced by BPDE in human cells, 41 spontaneous and 44 BPDE-induced mutant clones have been characterized using the Southern blot technique. In addition, rearrangements of the T-cell-receptor beta and gamma loci have been used to determine the proportion of isolated clones that are unique, and thus likely to represent independent mutational events. Out of 23 independent spontaneous mutants 4 had large hprt alterations that could be detected on Southern blots. Two of these alterations, deletions of exons 2-6, have been confirmed using PCR of hprt cDNA and direct sequencing of the PCR product. All 33 independent BPDE-induced mutants had normal hprt restriction patterns which indicates that BPDE is mainly a point mutagen in this system.

An exonic point mutation of the androgen receptor gene in a family with complete androgen insensitivity

We have discovered in the X-linked androgen receptor gene a single exonic nucleotide substitution that causes complete androgen insensitivity (resistance) in a sibship with three affected individuals. The mutation, a guanine-to-adenine transition, occurs at nucleotide number 2682 and changes the sense of codon 717 from tryptophan to a translation stop signal. Codon 717 is in exon 4, so the mutation predicts the synthesis of a truncated receptor that lacks most of its androgen-binding domain. The substitution abolishes a recognition sequence for the restriction endonuclease HaeIII. Amplification of exon 4 by the polymerase chain reaction followed by double digestion with HinfI and HaeIII permits facile recognition of hemizygotes and heterozygous carriers of the mutation.

Identification and Plant Interaction of a Phyllobacterium sp., a Predominant Rhizobacterium of Young Sugar Beet Plants

The second most abundant bacterium on the root surface of young sugar beet plants was identified as a Phyllobacterium sp. ( Rhizobiaceae ) based on a comparison of the results of 39 conventional identification tests, 167 API tests, 30 antibiotic susceptibility tests, and sodium dodecyl sulfate-polyacrylamide gel electrophoretic fingerprints of total cellular proteins with type strains of Phyllobacterium myrsinacearum and Phyllobacterium rubiacearum. It was found on 198 of 1,100 investigated plants between the 2nd and 10th leaf stage on three different fields in Belgium and one field in Spain. Densities ranged from 2 × 10 4 to 2 × 10 8 CFU/g of root. Five isolates exerted a broad-spectrum in vitro antifungal activity. DNA-DNA hybridizations showed that Phyllobacterium sp. does not contain DNA sequences that are homologous with the attachment genes chvA, chvB , the transferred-DNA (T-DNA) hormone genes iaaH and ipt from Agrobacterium tumefaciens, iaaM from A. tumefaciens and Pseudomonas savastanoi , or the nitrogenase genes nifHDK from Klebsiella pneumoniae. Phyllobacterium sp. produces indolylacetic acid in in vitro cultures and induces auxinlike effects when cocultivated with callus tissue of tobacco. When Phyllobacterium sp. was transformed with a Ti plasmid derivative, it gained the capacity to induce tumors on Kalanchoe daigremontiana. The potential role of Phyllobacterium sp. in this newly recognized niche is discussed.

An inter-Nordic prospective study on cytogenetic endpoints and cancer risk. Nordic Study Group on the Health Risk of Chromosome Damage

To investigate whether high rates of chromosomal aberrations (CAs), sister chromatid exchange (SCE), or micronuclei(MN) in peripheral lymphocytes indicate an increased risk for subsequent cancer, a prospective cohort study of 2,969 subjects cytogenetically examined between 1970 and 1988 in four Swedish, two Finnish, and two Norwegian laboratories was initiated. To standardize for the interlaboratory variation, the results of the three cytogenetic endpoints were trichotomized for each laboratory into "low" (1st to 33rd percentile), "medium" (34th to 66th percentile), and "high" (67th to 100th percentile]. Thirty-four cancers had been diagnosed in the cohort during the observation period (1970 to 1985). The point-estimates of the standardized morbidity ratio (SMR) in the three CA strata were 90, 92, and 180, respectively. This trend for a positive association was not statistically significant (p = 0.06). There was no significant trend between SMR and the trichotomized rates of SCE. In the subcohort examined for MN only two cases of cancer had been diagnosed until now. If subjects with "high" frequencies of CA or SCE have a two-fold (or greater) risk of developing cancer as compared with individuals who have "medium" or "low" frequencies, we estimate that there is a likelihood of 80% and 70%, respectively, that this will be detectable as significant (p less than or equal to 0.05) differences after a further follow-up period of 5 years. Weaker associations between cancer risk and the cytogenetic endpoints would not be possible to evaluate until even later follow-ups.

Levels of hypoxanthine phosphoribosyltransferase RNA in human cells

The gene for the purine salvage enzyme hypoxanthine phosphoribosyltransferase (HPRT) is expressed at a low level in many cells. As is the case with several other "housekeeping genes," thorough studies of hprt gene regulation have been hampered by the low levels of its mRNA. We have used RNA/RNA hybridization in solution to determine the concentration of hprt-RNA in human cells. The sensitivity and specificity of the method have been validated, and it is shown that hprt-RNA can be accurately determined at a level of a few mRNA molecules per cell. As expected for a housekeeping gene, low and relatively constant hprt-RNA levels (0.3-0.8 pg/micrograms DNA) were found in primary cultures of normal amnion cells and fibroblasts, EBV-transformed lymphoblastoid cell lines, neuroblastoma, glioblastoma, and melanoma cell cultures. While resting lymphocytes were found to contain very low amounts of hprt-RNA, lymphocytes stimulated with phytohemagglutinin (PHA) showed a 10-fold increase to about 0.8-1.2 pg/microgram DNA, which corresponds to 6-10 hprt-RNA molecules per cell. The level started to increase about 20 h after PHA stimulation, 5-10 h before the onset of DNA synthesis, and a steady-state level was reached after 2-3 days in culture. In PHA-stimulated lymphocytes from two brothers with inherited HPRT deficiency (Lesch-Nyhans syndrome), the hprt-RNA level in PHA-stimulated lymphocytes was only about 25% of that in normal subjects. In T-cells selected for HPRT deficiency by growth in 6-thioguanine medium, the levels of hprt-RNA were either normal or very low, which probably reflects the different nature of the mutations involved. These results demonstrate the sensitivity of this method for determinations of low levels of RNA and clearly show induction of hprt-RNA after mitogenic stimulation of human lymphocytes.

Recognition by the DNA repair system of DNA structural alterations induced by reversible drug-DNA interactions

Ditercalinium (NSC 335153) was synthesized as a bifunctional DNA intercalator. It is made of two 7-H pyridocarbazole rings joined by a rigid bis-ethyl bispiperidine chain. It binds to DNA with high affinity and elicits anti-tumor activity on a variety of animal tumors. 1H n.m.r. studies of ditercalinium bis-intercalated into d(CpGpCpG)2 have shown that the intercalation process occurs from the large groove of the DNA helix while the two intercalated rings are separated by two base pairs. Because of the linking chain rigidity of ditercalinium, DNA conformation has to be altered to permit the intercalation of the two rings. DNA must be bent toward the minor groove. In E. coli, ditercalinium elicits a specific toxicity on polA strains which is suppressed by an additional uvrA mutation. In vitro, the purified UvrA and UvrB proteins bind to the DNA-ditercalinium complex in an ATP dependent manner. The UvrABC complex induces single-strand nicks, but only when ditercalinium is bound to negatively supercoiled DNA. The life-time of the UvrAB-DNA-ditercalinium complex is greater than 50 min when free ditercalinium concentration is maintained constant in the incubation medium. The cytotoxicity of ditercalinium in E. coli results from the induction of a futile and abortive DNA repair. The reversible ditercalinium-DNA complex mimics a bulky DNA lesion, yet the UvrABC endonuclease is unable to cope with a reversible lesion since it cannot eliminate the causative agent. The interaction of UvrA and UvrB proteins has also been studied with DNA and other DNA-binding drugs forming high-affinity complexes such as distamycin. The Uvr protein recognition process appears to be associated with specific DNA structural alterations. In eukaryotic cells, ditercalinium is concentrated in mitochondria. Mitochondrial DNA is rapidly and totally degraded. Mitochondrial DNA coded proteins being no longer synthesized, the respiratory chain is progressively inactivated. The stimulation of the glycolytic pathway allows the cells to continue growth for several generations. Dihydro-orotate dehydrogenase is located in the inner membrane of mitochondria and its activity is dependent on mitochondria energization. It becomes inactive after ditercalinium treatment. A drop of the pyrimidine pool is then observed. Complementation of treated cells with uridine decreases 10-fold the ditercalinium toxicity. The cellular delayed toxicity of ditercalinium results from the slow induction of a pyrimidineless state associated with the progressive inactivation of mitochondria. The results show that DNA structural alterations induced by reversible drug-DNA complexes can be recognized by DNA repair enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)

Control by thyrotropin of the production by thyroid cells of an inositol phosphate-glycan

The increased turnover of phosphatidylinositol promoted by thyrotropin (TSH) in pig thyroid tissue does not seem to be caused by an increased production of inositol tris-phosphate. We have explored another possibility, the synthesis of an inositol phosphate-glycan (IP-gly). Our results show that thyroid cells in culture produced this substance from a precursor phosphatidylinositol-glycan (Gly-PI). The obtained IP-gly seemed, by its analytical and biological properties, to be identical, or similar, to the previously described insulin mediator.