Toxicity and mutagenicity of X-rays and [125I]dUrd or [3H]TdR incorporated in the DNA of human lymphoblast cells

We measured the toxicity and mutagenicity induced in human diploid lymphoblasts by various radiation doses of X-rays and two internal emitters. [¹²⁵I]iododeoxyuridine ([¹²⁵I]dUrd) and [³H]thymidine ([³H]TdR), incorporated into cellular DNA. [¹²⁵I]dUrd was more effective than [³H]TdR at killing cells and producing mutations to 6-thioguanine resistance (6TG^R). No ouabain-resistant mutants were induced by any of these agents. Expressing dose as total disintegrations per cell (dpc), the D₀ for cell killing for [¹²⁵I]dUrd was 28 dpc and for [³H]TdR was 385 dpc. The D₀ for X-rays was 48 rad at 37°C. The slopes of the mutation curves were approximately 75 × 10⁻⁸ 6TG^R mutants per cell per disintegration for [¹²⁵I]dUrd and 2 × 10⁻⁸ for [³H]TdR. X-Rays induced 8 × 10⁻⁸ 6TG^R mutants per cell per rad. Normalizing for survival, [¹²⁵I]dUrd remained much more mutagenic at low doses (high survival levels) than the other two agents. Treatment of the cells at either 37°C or while frozen at −70°C yielded no difference in cytotoxicity or mutation for [¹²⁵I]dUrd or [³H]TdR, whereas X-rays were 6 times less effective in killing cells at −70°C.

Assuming that incorporation was random throughout the genome, the mutagenic efficiencies of the radionuclides could be calculated by dividing the mutation rate by the level of incorporation. If the effective target size of the 6TG^R locus is 1000–3000 base pairs, then the mutagenic efficiency of [¹²⁵I]dUrd is 1.0–3.0 and of [³H]TdR is 0.02–0.06 total genomic mutations per cell per disintegration. ¹²⁵I disintegrations are known to produce localized DNA double-strand breaks. If these breaks are potentially lethal lesions, they must be repaired, since the mean lethal dose (D₀) was 28 dpc. The observations that a single dpc has a high probability of producing a mutation (mutagenic efficiency 1.0–3.0) would suggest, however, that this repair is extremely error-prone. If the breaks need not be repaired to permit survival, then lethal lesions are a subset of or are completely different from mutagenic lesions.     

5-Azacytidine inhibits the induction of transient TK-deficient cells by 5-bromodeoxyuridine. A novel hypothesis for the facilitation of hypermethylation by 5-bromodeoxyuridine.

This paper examines the mechanism by which 5-bromodeoxyuridine (BrdUrd) induces a high frequency of transient trifluorothymidine (F3TdR)-resistant variants in the TK6 human lymphoblast cell line (a TK +/- heterozygote). This phenomenon has previously been termed 'pseudomutation' (Liber et al., 1985). We now report that 5-azacytidine (5-AzaC), an inhibitor of DNA methylation, reverses BrdUrd-induced pseudomutation in a dose-dependent manner. The inhibition by 5-AzaC is highly specific and does not appear to involve nucleotide pool perturbations. 5-AzaC inhibits the pseudomutagenic effect (transient trifluorothymidine resistance in a thymidine kinase heterozygote), but not the stable mutagenic effect (stable 6-thioguanine resistance or trifluorothymidine resistance in a hypoxanthine-guanine phosphoribosyltransferase-proficient cell) induced by BrdUrd. 5-AzaC did not affect the induction nor expression of mutation induced by several other chemical mutagens at either the tk or hgprt loci. Inhibition of pseudomutation by 5-AzaC did not appear to be caused by a number of potential confounding factors. Although significant changes in the levels of DNA methylation were detected by HPLC analysis in BrdUrd-treated cells, the dose response for inhibition of pseudomutation by 5-AzaC was correlated with a significant decrease in 5-methylcytidine levels. These results and additional data in the literature have led us to postulate a novel mechanism in which the substitution of BrdUrd in a TpG dinucleotide(s) may serve as a substrate for non-heritable methylation and hence transiently inactivate tk gene expression.     

Influence of confluent holding time on UV light mutagenesis in human diploid fibroblasts

We have investigated the induction of mutants resistant to 6-thioguanine (6TG) following 254 nm ultraviolet light exposure of density-inhibited cultures of human diploid fibroblasts. Phenotypic expression of 6TG resistance was maximal within 9 days and remained stable through 19 days after irradiation. In reconstruction studies, complete recovery of 6TG-resistant mutants occurred at cell densities of up to 35 000 cells per 100-mm petri dish. The induced mutation frequency increased linearly with dose over the range of 3–9 J/m²; the D₀ of the survival curve was 4.2 J/m². Delaying subculture to low density for 1.5–24 h after irradiation produced unexpected alterations in induced mutation frequencies. An increase in UV-induced mutations of approximately 3-fold was observed in cultures maintained in confluence for 3 h. This trend was reversed with longer holding times: the mutation frequency declined sharply in cultures held for 6 h compared to the 3-h value, and thereafter showed a steady and gradual diminution to background levels.

These data suggest that the repair of potentíally mutagenic damage is a complex phenomenon which can lead to an increase or decrease in mutation frequency as a function of holding time. Although the decline in mutation frequency observed following longer holding intervals is consistent with the notion of an error-free process, we hypothesize that the increased mutation frequency produced by a short holding period reflects the existence of a cell-mediated process which enhances the mutagenic potential of at least some UV-induced DNA photoproducts.     

New mutations affecting induced mutagenesis in yeast

Previously isolated mutations in baker's yeast, Saccharomyces cerevisiae, that impair induced mutagenesis were all identified with the aid of tests that either exclusively or predominantly detect base-pair substitutions. To avoid this bias, we have screened 11 366 potentially mutant clones for UV-induced reversion of the frameshift allele, his4–38, and have identified 10 mutants that give much reduced yields of revertants. Complementation and recombination tests show that 6 of these carry mutations at the previously known REV1, REV1 and REV3 loci, while the remaining 4 define 3 new genes, REV4 (2 mutations), REV5 and REV6. The rev4 mutations are readily suppressed in many genetic backgrounds and, like the rev5 mutation, impart only a limited deficiency for induced mutagenesis: it is likely, therefore that the REV4⁺ and REV5⁺ gene functions are only remotely concerned with this process. The rev6 mutants have a more general deficiency, however, as well as marked sensitivity to UV and an increased spontaneous mutation rate, properties that suggest the REV6 gene is directly involved in mutation induction. The REV5 gene is located about 1 cM proximal to CYC1 on chromosome X.     

The number and localisation of adenine nucleotide-binding sites in beef-heart mitochondrial ATPase (F1) determined by photolabelling with 8-azido-ATP and 8-azido-ADP

1. When irradiated 8-azido-ATP becomes covalently bound (as the nitreno compound) to beef-heart mitochondrial ATPase (F₁) as the triphosphate, either in the absence or presence of Mg²⁺, label covalently bound is not hydrolysed.

2. In the presence of Mg²⁺ the nitreno-ATP is bound to both the and β subunits, mainly (63%) to the subunits.

3. After successive photolabelling of F₁ with 8-azido-ATP (no Mg²⁺) and 8-azido-ADP (with Mg²⁺) 4 mol label is bound to F₁, 2 mol to the and 2 mol to the β subunits.

4. When the order of photolabelling is reversed, much less 8-nitreno-ATP is bound to F₁ previously labelled with 8-nitreno-ADP. It is concluded that binding to the -subunits hinders binding to the β subunits.

5. F₁ that has been photolabelled with up to 4 mol label still contains 2 mol firmly bound adenine nucleotides per mol F₁.

6. It is concluded that at least 6 sites for adenine nucleotides are present in isolated F₁.     

Effect of the homokaryotic or heterokaryotic state of the uvs-2 allele in Neurospora crassa on mitomycin C-induced killing and ad-3 mutation

Mitomycin C (MC) was tested for its killing and mutagenic activities in the ad-3 forward-mutation test in Neurospora crassa. The test was conducted in 4 dikaryons of N. crassa in order to determine the effect of the uvs-2 allele, which causes a defect in nucleotide excision repair, on MC-induced killing and ad-3 mutation. These dikaryons were homokaryotic for uvs-2⁺ (H-12), homokaryotic for uvs-2 (H-59), and heterokaryotic for uvs-2/uvs-2⁺ (H-70 and H-71). MC induced killing and ad-3 mutation in H-12, but the presence of uvs-2 in the homokaryotic state (H-59) resulted in a great increase in the killing and mutagenic activities of MC. This increased sensitivity to MC-induced killing and mutation conferred by uvs-2 in the homokaryotic state (H-59 vs. H-12) is a different effect than that noted by others for a defect in nucleotide excision-repair in Escherichia coli and Salmonella typhimurium or in human cells. The dikaryons heterokaryotic for uvs-2/uvs-2⁺ had the same sensitivity to MC as H-12, indicating that for MC-induced killing and ad-3 mutation uvs-2 is recessive to uvs-2⁺.     

Analysis of hexamethylphosphoramide (HMPA)-induced genetic alterations in relation to DNA damage and DNA repair in Drosophila melanogaster

This paper reports the results of a study on the mutagenic profile of HMPA in Drosophila melanogaster. HMPA produced all types of genetic damage tested for in post-meiotic cells of treated males; at the concentrations used, recessive lethals and ring-X losses were induced at significant rates while 2–3 translocations, entire and partial Y-chromosome losses only occurred at low rates. From a comparison with alkylation-induced mutational spectra, we note a number of peculiarities of HMPA mutagenesis:

1. (1) there is no storage effect on HMPA-induced translocations;

2. (2) the ratio of F₂-lethals: F₃-lethals varies from 6 : 1 to 9 : 1, indicating a low capacity of HMPA for delayed mutations;

3. (3) the use of the DNA-repair-deficient mei-9^L1 females instead of an excision-proficient control strain has no influence on the recovery of mutations )recessive lethals) induced in males;

4. (4) the high frequencies of chromosome loss (CL) induced by HMPA, which are mostly due to ring-X loss, leads us to speculate that one (or more) of its metabolites acts as a DNA-crosslinking agent. In experiments on maternal effects with mei-9^L1 females, there is a 20–40% reduction in the rates of induced CL. Conversely, with mei-41^D5 females, there is a weak increase in CL frequencies.

5. (5) HPLC analysis of DNA reacted with [¹⁴C]HMPA exhibits no methylation at the O⁶ or the N-7 of guanine. This finding, together with the observed inactivity of hexaethylphosphoramide (HEPA) in the recessive lethal assay, suggests that the formation of DNA-bound forms from HMPA may not be the result of simple methylation reactions. This conclusion is supported by the genetic data, i.e., the lack of a storage effect on HMPA-induced chromosome rearrangements.

Consistent with a hypothesis by Brodberg et al. (1983) to explain the action of cisplatin in Drosophila, comparisons of the spectra of genetic alterations produced by HMPA, A 139 (bifunctional) and Thio-TEPA (trifunctional) in the assay for chromosome loss suggest the involvement of two distinct mechanisms in the formation of ring-X loss by crosslinking agents. One pathway concerns induction of chromosome loss as a consequence of sister-chromatid exchanges (SCEs). The second mechanism may be due to DNA adducts or a single adduct responsible for both a fraction of CL and for induced partial Y-loss (PL). Inactivation of the mei-9⁺ function has two consequences: SCE-mediated ring-X loss frequency is lowered in mei-9 females in comparison to the repair-proficient control strain, while the opposite effect is indicated for that fraction of ring-X loss generated by the second mutational pathway. Additional complicating factors include the observation of a dual role of storage in our study: the proportion of SCE-related chromosome losses decreases with increasing time of storage, but that produced by the alternative pathway increases. Thus, the CL frequencies actually recorded under the heading ‘chromosome loss’ appear as the net result of two mechanisms counteracting each other in their effects.     

Effect of O6-alkylguanine-DNA alkyltransferase on the frequency and spectrum of mutations induced by N-methyl-N''-nitro-N-nitrosoguanidine in the HPRT gene of diploid human fibroblasts

N-Methyl-N′-nitro-N-nitrosoguanidine (MNNG) reacts with 12 nucleophilic sites in DNA to induce a variety of lesions, but O⁶-methylguanine (O⁶-MeG) and O⁴-methylthymine are the most effective premutagenic lesions produced, mispairing with thymine and guanine, respectively. O⁶-MeG is repaired by O⁶-alkylguanine-DNA alkyltransferase (AGT), which removes the methyl group from the O⁶ position and transfers it to itself, rendering the transferase inactive. When diploid human fibroblasts were exposed to 25 μM, O⁶-benzylguanine (O⁶-BzG) in the medium for 3 h, their level of AGT activity was dramatically reduced, to a level of at most 1.6% of the control. Populations of cells pretreated with this level of O⁶-BzG for 2 h or not pretreated, were exposed to MNNG at a concentration of 2, 4 or 6 μM in the presence or absence of O⁶-BzG and assayed for survival of colony-forming ability and the frequency of 6-thioguanine-resistant cells (mutations induced in the HPRT gene). O⁶-BzG (25 μM) was also present in the appropriate half of the cells during the 24 h immediately follwing exposure to MNNG. This 27-h exposure to O⁶-BzG alone had no cytotoxic or mutagenic effect on the cells but significantly increased the cytotoxicity and mutagenecity of MNNG, increasing the mutant frequency to that found previously in human cells constitutively devoid of AGT activity. At doses of 2 μM and 4 μM MNNG, the mutant frequency observed with the AGT-depleted cells was 120 × 10⁻⁶ and 240 × 10⁻⁶, respectively; in the cells with abundant AGT activity, these values were 10 × 10⁻⁶ and 20 × 10⁻⁶, respectively. DNA-sequence analysis of the coding region of the HPRT gene in 36 independent mutants obtained from MNNG-treated AGT-depleted populations and 36 from the control populations showed that even though AGT repair lowered the frequency of mutants by more than 90%, it did not affect the kinds of mutations induced by MNNG nor the strand distribution of the premutagenic guanine lesions. In mutants from the AGT-depleted cells, there were 26 base substitutions and 13 putative splice site mutations; in the control, there were 25 base substitutions and 11 splice site mutations. All but two substitutions involved G · C with 92% being G · C → A · T. In both sets, of the premutagenic lesions were located in the nontranscribed strand. Many ‘hot spots’ were seen, and there was evidence that AGT repaired more lesions from the 5′ half of the gene than from the 3′ half.     

Effects of peptide YY and its analogues on chloride ion secretion in fed and fasted rat jejunum

The aim of our study was to determine whether a meal modifies the antisecretory response induced by PYY and the structural requirements to elicit antisecretory effects of analogue PYY(22–36) for potential antidiarrhea therapy. The variations in short-circuit current (Isc) due to the modification of ionic transport across the rat intestine were assessed in vitro, using Ussing chambers. In fasted rats, PYY induced a dose- and time-dependent reduction in Isc, with a sensitivity threshold at 5 × 10⁻¹¹ M (ΔIsc −2 ± 0.5 μA/cm²). The reduction was maximal at 10⁻⁷ M (Isc −23 ± 2 μA/cm²), and the concentration producing half-maximal inhibition was 10⁻⁹ M. At 10⁻⁷ M, reduction of Isc by PYY reached 90% of response to 5 × 10⁻⁵ M bumetanide. The PYY effect was partly reversed by 10⁻⁵ M forskolin (Isc +13.43 ± 2.91 μA/h·cm², p < 0.05) or 10⁻³ M dibutyryl adenosine 3′,5′ cyclic monophosphate (Isc +12 ± 1.69 μA/cm², p < 0.05). Naloxone and tetrodotoxin did not alter the effect of PYY. In addition, PYY and its analogue P915 reduced net chloride ion secretion to 2.85 and 2.29 μEq/cm² (p < 0.05), respectively. The antisecretory effect of PYY was accompanied by dose- and time-dependent desensitization when jejunum was prestimulated by a lower dose of peptide. The antisecretory potencies exhibited by PYY analogues required both a C-terminal fragment (22–36) and an aromatic amino acid residue (Trp or Phe) at position 27. At 10⁻⁷ M the biological activity of PYY was lower in fed than fasted rats (p < 0.001). Our results confirm the antisecretory effect of PYY, but show that the fed period is accompanied by desensitization, similar to the transient desensitization observed in the fasted period with cumulative doses. This suggests that PYY may act as a physiological mediator that reduces intestinal secretion.     

Effect of growth hormone and γ-aminobutyric acid on Brachionus plicatilis (Rotifera) reproduction at low food or high ammonia levels

Growth hormone (GH, 0.0025 and 0.025 I.U. ml⁻¹) and γ-aminobutyric acid (GABA, 50 μg ml⁻¹) enhance rotifer population growth in batch cultures. In order to further understand the mechanism of their actions, we conducted experiments culturing isolated females at low food and high free ammonia levels. At an optimum food level of 7×10⁶ Nannochloropsis oculata cells ml⁻¹ or at low free ammonia level of 2.4 μg ml⁻¹, the F₁ offspring of rotifers treated with GH at 0.0025 I.U. ml⁻¹ had significantly higher population growth rate (r) and net reproduction rate (Ro), and shorter generation time than untreated rotifers. At a lower food level of 7×10⁵ cells ml⁻¹ or at high free ammonia level of 3.1 μg ml⁻¹, rotifers treated with GABA at 50 μg ml⁻¹ had significantly higher r and Ro, and shorter generation time. These results indicate that GABA is effective in enhancing rotifer reproduction when rotifers are cultured under stress whereas GH enhances rotifer reproduction when culture conditions are optimal. Significant effects were also observed in F¹ and F² generations which were not treated with hormones. These data may be useful for treating rotifer mass cultures to mitigate the effects of stress caused by high population densities.     

Induction of lacI mutations in Big Blue Rat-2 cells treated with 1-(2-hydroxyethyl)-1-nitrosourea: a model system for the analysis of mutagenic potential of the hydroxyethyl adducts produced by 1,3-bis (2-chloroethyl)-1-nitrosourea.

We have investigated the genotoxic effects of 1-(2-hydroxyethyl)-1-nitrosourea (HENU). We have chosen this agent because of its demonstrated ability to produce N7-(2-hydroxyethyl) guanine (N7-HOEtG) and O⁶-(2-hydroxyethyl) 2′-deoxyguanosine (O⁶-HOEtdG); two of the DNA alkylation products produced by 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU). For these studies, we have used the Big Blue Rat-2 cell line that contains a lambda/lacI shuttle vector. Treatment of these cells with HENU produced a dose dependent increase in the levels of N7-HOEtG and O⁶-HOEtdG as quantified by HPLC with electrochemical detection. Treatment of Big Blue Rat-2 cells with either 0, 1 or 5 mM HENU resulted in mutation frequencies of 7.2±2.2×10⁻⁵, 45.2±2.9×10⁻⁵ and 120.3±24.4×10⁻⁵, respectively. Comparison of the mutation frequencies demonstrates that 1 and 5 mM HENU treatments have increased the mutation frequency by 6- and 16-fold, respectively. This increase in mutation frequency was statistically significant (P<0.001). Sequence analysis of HENU-induced mutations have revealed primarily G:C→A:T transitions (52%) and a significant number of A:T→T:A transversions (16%). We propose that the observed G:C→A:T transitions are produced by the DNA alkylation product O⁶-HOEtdG. These results suggest that the formation of O⁶-HOEtdG by BCNU treatment contributes to its observed mutagenic properties.     

High resolution genetic and physical mapping of the mouse asebia locus: A key gene locus for sebaceous gland differentiation

The asebia (ab) mutation in the mouse is an autosomal recessive trait with hypoplastic sebaceous glands. As a first step toward cloning the ab gene, we report here the genetic mapping of the ab locus with respect to Chromosome 19 microsatellite markers. 644 backcross progeny were generated by mating (CAST/EiJ × DBA/1LacJ-ab^2J/ab^2J) F₁ heterozygous females and parental ab^2J/ab^2J mutant males. Our results located the ab gene to an interval of 1.6 cM on mouse Chromosome 19 defined by flanking markers D19Mit11 and D19Mit53/D19Mit27, and identified a tightly linked polymorphic marker, D19Mit67, that co-segregates with the mutation in the backcross progeny examined. This places ab locus 4 cM distal to its present position as indicated in Mouse Genome Database at The Jackson Laboratory. We have also mapped a yeast artificial chromosome (YAC) contig in this locus interval which suggests the ab interval to be less than one megabase of DNA.     

A model for the involvement of Okazaki fragments maturation in the expansion of short tandem repeats

Mutations were accumulated with a wide variety in the p53 pseudogene of various wild mouse species and subspecies captured at different localities, as extensively observed in the exon 4 – exon 5 region. The rate of mutation accumulation in the mouse p53 pseudogene was estimated to be 1.4–2.1×10⁻⁸ mutations/bp/year, which is 20–30 times faster than that of the functional p53 and makes the dating possible for the time range of 10⁶ years or more. From comparison of the mutation spectrum, the origin of laboratory mice was identified to one of two M. m. domesticus groups.     

Mutation induction by okadaic acid, a protein phosphatase inhibitor, in CHL cells, but not in S. typhimurium.

Okadaic acid (OA) is a specific and strong inhibitor of protein phosphatase 1 and 2A present in eukaryotes, and a potent promoter of carcinogenesis in mouse skin. In this study, we examined the mutagenicity of OA. OA did not induce mutations in S. typhimurium TA100 and TA98, with or without a microsomal metabolic activation system. However, it was strongly mutagenic to Chinese hamster lung (CHL) cells without a microsomal activation system, as shown using diphtheria toxin (DT) resistance (DT^r) as a selective marker. Treatment of CHL cells with OA at 17.5 ng/ml induced 164 DT^r mutants per 10⁶ survivors. A plot of the mutation frequency against the OA concentration gave a concave curve, and the mutant frequency was calculated to be 5500/10⁶ survivors/μg, with OA in the dose range of 10–15 ng/ml. This value was about 680 times that of ethyl methanesulfonate (EMS), and comparable to that of 2-amino-N⁶-hydroxyadenine, one of the strongest knowon mutgens. Elongation factor 2 (EF-2) obtained from 4 DT^r clones was not ADP-ribosylated by DT fragment A. PCR-direct sequencing revealed that the hot spot of EF-2 for EMS mutagenesis in CHO-K1 cells, the first letter of codon 717, was not a t spot for OA mutagenesis in CHL cells.     

Determination of bacterial cell number and cell volume by means of flow cytometry, transmission electron microscopy, and epifluorescence microscopy

Comparative measurements of bacterial total counts and volumes of flow cytometry (FCM), transmission electron (TEM), and epifluorescence microscopy (EFM), were undertaken during a four week mesocosm experiment. Total counts of bacteria measured by TEM, EFM, and FCM were in the range of 1 · 10⁶−6 cells ml⁻¹, 1 · 10⁶−3 · 10¹⁶ cells ml⁻¹, and 5 · 10⁵ cells ml⁻¹ respectively. The mean volume of the bacterial community, measured by means of EFM and TEM, increased from 0.12–0.15 μm³ at the start of the experiment to 0.39–0.53 μm³ at the end. Generally, there was good agreement between the two methods and regression analyses gave r = 0.87 (p < < 0.01) for cell volume and r = 0.97 (p < < 0.01) for cell number. DAPI stained bacteria with volumes less than 0.2 μm³ were not detected by flow cytometry and these were generally an order of magnitude lower than counts made by TEM and EFM. For samples where the mean bacterial cell volume was longer than 0.3 μm³, all three methods were in agreement both with respect to counts and volume estimates.     

斑马鱼tbx2b调控心脏房室间隔发育的功能研究*

tbx2是早期心脏发育的关键基因。为进一步探究其对房室间隔(AVC)发育的影响,研究利用CRISPR/Cas9介导的基因敲除技术,成功构建了斑马鱼tbx2b突变体。通过T7E1酶切对其F₀进行敲除效率检测,结果显示平均敲除效率约为57.5%。F₁进一步筛选获得tbx2b杂合突变体,测序结果显示突变类型为11 bp碱基缺失的移码突变。tbx2b杂合子内交获得纯合子,tbx2b纯合突变体在5 dpf死亡并出现早期心脏环化异常表型。斑马鱼整胚原位杂交实验显示在3 dpf tbx2b纯合突变体中, 心脏腔室分化特异性标志基因nppa、nppb表达上调并异位表达在AVC,而AVC发育关键基因has2的表达消失。高效构建tbx2b突变体并初探其对下游基因的影响,为后续深入研究tbx2b对心脏AVC发育的作用奠定了基础,同时加深了人们对早期心脏调控网络的认识。     

Induction of specific-locus and dominant lethal mutations in male mice by 1-methyl-1-nitrosourea (MNU)

1-Methyl-1-nitrosourea (MNU) induced specific-locus mutations in mice in all spermatogenic stages except spermatozoa. After intraperitoneal injection of 70 mg/kg body weight of MNU a high yield of specific-locus mutations was observed in spermatids (21.8 × 10⁻⁵ mutations per locus per gamete). The highest mutational yield was induced in differentiating spermatogonia. In 1954 offspring we observed 5 specific-locus mutants (44.8 × 10⁻ mutations per locus per gamete). In addition, 2 mosaics were recovered, which gave a combined mutation rate of 62.7 × 10⁻⁵. In A_s spermatogonia the mutation rate was 3.9 × 10⁻⁵. The same dose of 70 mg/kg of MNU induced dominant lethal mutations 5–48 days post treatment, mainly due to post-implantation loss in spermatids and spermatocytes. It is interesting to compare the induction pattern of mutations by MNU with methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS) and ethylnitrosourea (ENU). Based on the different spermatogenic response of the induction of specific-locus mutations we can characterize the 4 mutagens in the following way: EMS = MMS ≠ MNU ≠ ENU.     

Application of the hydro(solvo)thermal technique to the synthesis of metal carbonyl chalcogenide clusters Part 3. Synthesis, structural characterization, and spectroscopic studies of the clusters [{M(CO)4}n(MS4)] (M = Mo, W; N=1, 2)

The methanothermal reactions of M(CO)₆ (M = Mo, W) with Na₂S₂ gave a series of homonuclear clusters [{M(CO)₄}_n(MS₄)]²⁻ (M=Mo, W; N=1, 2), i.e. (Ph₄P)₂[(CO)₄Mo(MoS₄)] (I), (Ph₄P)₂[(CO)₄W(WS₄)] (II), (Ph₄P)₂[(CO)₄Mo(MoS₄)Mo(CO)₄] (III) and (Ph₄P)₂[(CO)₄W(WS₄)W(CO)₄] (IV). The two dimers, I and II, as well as the two trimers, III and IV, are isostructural to each other, respectively. All compounds crystallize in the triclinic space group with Z=2. The cell dimensions are: a=12.393(8), b=19.303(9), c=11.909(6) Å, =102.39(5), β=111.54(5), γ=73.61(5)°, V=2522(3) ų at T=23 °C for I; a=12.390(3), b=19.314(4), c=11.866(2) Å, =102.66(2), β=111.49(1), γ=73.40(2)°, V=2511(1) ų at T=23 °C for II; a=11.416(3), b=22.524(4), c=10.815(4) Å, =91.03(2), β=100.57(3), γ=88.96(2)°, V=2733(1) ų at T=−100 °C for III, a=11.498(1), b=22.600(4), c=10.864(3) Å, =90.92(2), β=100.85(1), γ=88.58(1)°, V=2771(2) ų at T=23 °C for IV. The dimers are each formed by the coordination of the tetrathiometalate as a bidentate chelating ligand to an M(CO)₄ fragment while addition of another M(CO)₄ fragment to the dimers results in the trimers. All compounds contain both tetrahedral and octahedral metal centers with the formal 6+ and 0 oxidation states, respectively.     

Chemical synthesis of an artificial antigen containing the trisaccharide hapten of Mycobacterium leprae

The crystal and the molecular structure of 4,1′,6′-trichloro-4,1′,6′-trideoxy-galacto-sucrose (TGS) was determined by X-ray analysis at 294 K. Crystals of TGS are orthorhombic, space group P2₁2₁2₁, with a = 7.318(3), b = 12.027(4), c = 18.136(5) Å, V = 1596(1) ų, Z = 4; D_x = 1.655 g.cm^-3, λ(MoK) = 0.71073 Å, μ(MoK) = 5.44 cm^-1, F(000) = 816. The X-ray intensities of 2649 reflections with I 2.5σ(I) were measured with Zr-filtered MoK-radiation. The structure was solved by the Patterson procedure and refined by full-matrix least-squares to a final R-value of 0.0298. Large conformational differences between TGS and sucrose were observed, particularly in the conformation of the glycosidic linkage. These differences originate from chlorine substitution, which affects intramolecular hydrogen bonding and sweet-taste glucophores.