Identification of a pterin derivative in Escherichia coli DNA photolyase

DNA photolyase from Escherichia coli contains reduced flavin adenine dinucleotide plus a second chromophore, partially characterized in previous studies. Both chromophores function as sensitizers in catalysis. The second chromophore has been identified as a 6-substituted pterin derivative. The compound is oxidized with permanganate to yield 6-carboxypterin or reduced with sodium cyanoborohydride to yield a 5,6,7,8-tetrahydropterin derivative. The second chromophore exhibits spectral properties (lambda max = 360, 255 nm, pH 2) similar to that observed for 7,8-dihydropterin cations. The compound does not exhibit a spectrally detectable pKa around 4 but is converted to a dication (lambda max = 346, 255 nm) in strong acid (pKa approximately 1). Similar ionization behavior is observed with 7,8-dihydropterin derivatives that are alkylated at N(5). The instability of the second chromophore in weakly alkaline solution is due to a fully reversible conversion to a labile bleached form. As compared with other pterin derivatives, the hydrolytic instability is unusual but is very similar to that observed for 5,6-dialkyl-7,8-dihydropterinium salts. It is proposed that the second chromophore is a 7,8-dihydropterin with substituents at positions 5 and 6. The discovery that a pterin derivative functions as a photosensitizer in DNA repair is apparently the first example of a photobiological function for pterins.     

Fatty acid synthesis in the fetal lung: relationship to surfactant lipids

The aims of this study were to investigate the control of fatty acid synthesis and its relationship to surfactant production in the fetal lung during alteration of hormonal and substrate conditions. Lung explants from 18 day fetuses (term = 22 days) which were cultured 2 days in the presence of 10 mM lactate showed parallel acceleration of de novo fatty acid synthesis (3H2O incorporation) and [14C]choline incorporation into disaturated phosphatidylcholine (DSPC) compared to culture of explants in glucose. Both the cultured and fresh explants were resistant to the classical short term (4 h) cAMP inhibition of fatty acid synthesis with 3 mM dibutyryl cAMP or 0.5 mM aminophylline. In the cultured explants short term cAMP elevation increased DSPC production, and long term (2 day) cAMP elevation caused a further increase in DSPC synthesis and also stimulated fatty acid synthesis. In cultured explants from 17 day fetuses, dexamethasone (0.1 microM) caused a synergistic increase with aminophylline in both fatty acid synthesis and DSPC production whereas, in explants from 18 day fetuses, dexamethasone inhibited both processes and reduced the level of stimulation of DSPC and fatty acid synthesis seen with aminophylline alone. Dexamethasone also reduced the stimulation of both DSPC and fatty acid synthesis produced in the culture of 18 day explants with bacitracin (0.5 mg/ml), whereas the combination of bacitracin and aminophylline resulted in a synergistic increase in DSPC production. Culture with glucagon (0.1 microM) also stimulated DSPC synthesis but at physiological levels insulin had no effect on either DSPC or fatty acid synthesis. These data show that lung fatty acid synthesis exhibits unique features of fatty acid synthesis regulation compared to other lipogenic tissues and also suggest a link between de novo fatty acid synthesis and surfactant production during the critical period of accelerated lung maturation.     

Regional localization of DNA sequences on chromosome 21 using somatic cell hybrids.

We have used a panel of Chinese hamster X human somatic cell hybrids, each containing various portions of chromosome 21 as the only detectable human chromosome component, for regional mapping of cloned, chromosome 21-derived DNA sequences. Thirty unique and very low-repeat sequences were mapped to the short arm and three sections of the long arm. Three unique sequences map to the proximal part of the terminal band 21q22.3, and five to the distal part of this band. Some of these may represent parts of gene sequences that may be relevant to the pathogenesis of Down syndrome, as 21q22 is the area required to be present in triplicate for the full clinical picture.     

The equine protease inhibitory system (Pi): Abnormal expressions of PiF,PiL, and PiS

Three cases of abnormal expression of the equine protease inhibitory alleles, Pi F, L, and S₁, were observed following the examination of 30,000 plasma samples by one-dimensional acid (pH 4.6) polyacrylamide gel electrophoresis. Characterization of the abnormal proteins in terms of isoelectric point, molecular mass, inhibitory spectra, and sialic acid content was performed using one- and two-dimensional electrophoretic techniques. The Pi F and S₁ abnormalities were postulated to be the result of amino acid substitutions causing alterations in the processing of the carbohydrate side chains. No explanation could be offered for the Pi L abnormality other than a charge shift mutation. Abnormal types, F*, L*, and S*₁ behaved as alleles but the distribution of L* in offspring from one stallion (present in only 6 of 83 offspring) differed significantly from expectation.This work was supported by a grant from the Australian Stud Book, Alison Road, Randwick, N.S.W. 2031.     

H2-restricted recognition of cloned HLA class I gene products expressed in mouse cells

Long-term syngeneic mouse cytolytic T lymphocyte (CTL) clones were obtained from DBA/2 (H2d) mice immunized with P815 (H2d) cells transfected with cloned human class I histocompatibility genes, HLA-CW3 or HLA-A24. Three distinct patterns of specificity were defined on P815 HLA transfectant target cells. One clone lysed HLA-CW3 but not -A24 transfectants, and a second lysed HLA-A24 but not -CW3 transfectant target cells. The third clone lysed P815 targets transfected with either HLA gene. None of the CTL clones lysed L cells (H2k) transfected with the same HLA genes or human targets that expressed these HLA specificities. Several lines of evidence indicated that recognition of HLA transfectants by these CTL clones was H2 restricted. First, lysis of P815 HLA transfectants could be inhibited by anti-H2Kd monoclonal antibody. In addition, the anti-P815-HLA CTL clones could lyse a (human X mouse) hybrid target that expressed both HLA class I and H2Kd antigens, but not a clonal derivative that no longer expressed H2Kd. The most direct evidence for H2-restricted recognition of P815-HLA transfectants by the syngeneic CTL clones was obtained by double transfection of mouse L cells (H2k) with both HLA and H2 class I genes. L cells transfected with HLA and H2Kd genes were susceptible to lysis by the same CTL clones that lysed the corresponding P815-HLA transfectant targets. Thus under certain conditions, CTL recognition of xenogeneic class I histocompatibility gene products can be restricted by other class I gene products.     

Localization of the human NCAM gene to band q23 of chromosome 11: the third gene coding for a cell interaction molecule mapped to the distal portion of the long arm of chromosome 11

cDNA clones containing sequences coding for the murine neural cell adhesion molecule (N-CAM) were used in Southern hybridizations on human genomic DNA and demonstrated approximately 90% homology between human and murine NCAM genes. In situ hybridization with one of these clones was performed on human metaphase chromosomes and allowed the localization of the human NCAM gene to band q23 of chromosome 11. The genes for two other cell surface molecules believed to be involved in cell-cell interactions, Thy-1 and the delta chain of the T3-T cell receptor complex, have recently been localized to the same region of chromosome 11 in man. Moreover, this region of the human chromosome 11 appears to be syntenic to a region of murine chromosome 9 that also contains the staggerer locus: staggerer mice show abnormal neurological features which may be related to abnormalities in the conversion of the embryonic to the adult forms of the N-CAM molecule.     

Molecular cloning and DNA sequence analysis of genes encoding cytotoxic T lymphocyte-defined HLA-A3 subtypes: the E1 subtype

Influenza-specific cytotoxic T cells restricted by HLA-A3 and allogeneic CTL specific for HLA-A3 recognize differences between serologically indistinguishable HLA-A3 antigens. Previous biochemical studies have indicated that such differential recognition can be explained by alterations in the primary structure of class I heavy chains. Characterization of these sequence differences may therefore identify portions of the class I molecule that form determinants recognized by CTL. In this study, we describe the cloning and sequencing of an HLA-A3 subtype from donor E1 (E1-A3). Cloning of the gene encoding E1-A3 was simplified by determining that a 15.5-kb BamHI fragment contains the complete gene and is characteristic of HLA-A3 and only one other class I gene (HLA-A11). Comparison of the E1-A3 sequence to that of a previously sequenced HLA-A3 gene for exons encoding extracellular class I domains revealed three nucleotide differences. All of these differences were located within a discrete region of exon 3 (encoding the alpha 2 domain) and result in a change of two amino acids, at positions 152 (Glu----Val) and 156 (Leu----Gln). This finding suggests that these amino acids are crucial for the information of a determinant recognized by CTL. Furthermore, the altered nucleotide sequence of E1-A3 is identical to the sequence of the HLA-Aw24 gene for codons 128 to 161. These observations of multiple clustered changes in the E1-A3 subtype (relative to the prototype sequence) and identity of the altered sequence with the sequence of another class I gene support the concept that gene conversion is a primary mechanism for the generation of class I polymorphism.     

1,25-Dihydroxyvitamin D3 suppresses human T helper/inducer lymphocyte activity in vitro

The active form of vitamin D3, 1 alpha,25-dihydroxyvitamin D3 (1,25-(OH)2-D3), suppresses in vitro immunoglobulin (Ig) production by activated peripheral blood mononuclear cells (PBM) from normal human subjects by inhibiting T helper/inducer TH cell activity. Normal PBM were fractionated into B, TH and T suppressor/cytotoxic (Ts) cells by fluorescence-activated cell sorting techniques. The resultant subsets were activated with mitogens and were cultured in the presence or absence of a receptor-saturating concentration of 1,25-(OH)2-D3. The sterol reduced [3H]thymidine incorporation in TH cells by 56%, with no effect on Ts or B cells. When 1,25-(OH)2-D3-treated TH cells were co-cultured with untreated B cells and culture supernatants assayed for Ig production, 1,25-(OH)2-D3 abrogated the inducing effect of TH cells on Ig synthesis by B cells. There was no inhibitory effect of the sterol on Ts or B cell activity. In addition, 1,25-(OH)2-D3 produced a dramatic inhibition of interleukin 2 (IL 2) production by activated PBM, but did not inhibit IL 2 receptor generation by these cells. Other vitamin D metabolites tested did not produce this effect. These results suggest that the TH lymphocyte is the specific cellular target for the immunoinhibitory effects of 1,25-(OH)2-D3.     

Hepatotoxic doses of dioxin do not damage mouse bone marrow chromosomes

We report on a study of the cytogenetic and hepatotoxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Mice of the C57B1/6J (with high-affinity TCDD receptor) or DBA/2J (with low-affinity TCDD receptor) strains were given single intraperitoneal injections of 50, 100 or 150 micrograms of TCDD/kg body weight. At various times (8-48 h) after injection, we examined bone marrow cells for cytogenetic effects by performing structural aberration, sister-chromatid exchange, and micronucleus tests. 1 month after exposure, liver sections were studied for hepatotoxic effects. We found no evidence of chromosome damage by TCDD given in doses that cause liver damage in both strains of mice.