Synthesis and characterization of stacked and quenched uridine nucleotide fluorophores.
Intramolecular aromatic interactions in aqueous solution often lead to stacked conformation for model organic molecules. This designing principle was used to develop stacked and folded uridine nucleotide analogs that showed highly quenched fluoroscence in aqueous solution by attaching the fluorophore 1-aminonaphthalene-5-sulfonate (AmNS) to the terminal phosphate via a phosphoramidate bond. Severalfold enhancement of fluorescence could be observed by destacking the molecules in organic solvents, such as isopropanol and dimethylsulfoxide or by enzymatic cleavage of the pyrophosphate bond. Stacking and destacking were confirmed by 1-H NMR spectroscopy. The extent of quenching of the uridine derivatives correlated very well with the extent of stacking. Taking 5-H as the monitor, temperature-variable NMR studies demonstrated the presence of a rapid interconversionary equilibrium between the stacked and open forms for uridine-5'-diphosphoro-beta-1-(5-sulfonic acid) naphthylamidate (UDPAmNS) in aqueous solution. DeltaH was calculated to be -2.3 Kcal/mol, with 43-50% of the population in stacked conformation. Fluorescence lifetime for UDPAmNS in water was determined to be 2.5 ns as against 11 ns in dimethyl sulfoxide or 15 ns for the pyrophosphate adduct of AmNS in water. Such a greatly reduced lifetime for UDPAmNS in water suggests collisional interaction between the pyrimidine and thefluorophore moieties to be responsible for quenching. The potential usefulness of such stacked and quenched nucleotide fluorophores as probes for protein-ligand interaction studies has been briefly discussed. (+info
Histidine 179 mutants of GTP cyclohydrolase I catalyze the formation of 2-amino-5-formylamino-6-ribofuranosylamino-4(3H)-pyrimidinone triphosphate.
GTP cyclohydrolase I catalyzes the conversion of GTP to dihydroneopterin triphosphate. The replacement of histidine 179 by other amino acids affords mutant enzymes that do not catalyze the formation of dihydroneopterin triphosphate. However, some of these mutant proteins catalyze the conversion of GTP to 2-amino-5-formylamino-6-ribofuranosylamino-4(3H)-pyrimidinone 5'-triphosphate as shown by multinuclear NMR analysis. The equilibrium constant for the reversible conversion of GTP to the ring-opened derivative is approximately 0.1. The wild-type enzyme converts the formylamino pyrimidine derivative to dihydroneopterin triphosphate; the rate is similar to that observed with GTP as substrate. The data support the conclusion that the formylamino pyrimidine derivative is an intermediate in the overall reaction catalyzed by GTP cyclohydrolase I. (+info
Nucleotide sequence of an RNA polymerase binding site from the DNA of bacteriophage fd.
The primary structure of a strong RNA polymerase binding site in the replicative form DNA of phage fd has been determined by direct DNA sequencing. It is: (see article). The molecule contains regions with 2-fold symmetry and sequence homologies to promoter regions from other DNAs. The startpoint of transcription is located in the center of the binding site. (+info
A search for base analogs to enhance third-strand binding to 'inverted' target base pairs of triplexes in the pyrimidine/parallel motif.
Eight base analogs were tested as third strand residues in otherwise homopyrimidine strands opposite each of the 'direct' (A.T and G.C) and 'inverted' (T.A and C.G) Watson-Crick base pairs, using UV melting profiles to assess triplex stability. The target duplexes contained 20 A.T base pairs and a central test base pair X.Y, while the third strand contained 20 T residues and a central Z test base. Z included 5-bromo-uracil, 5-propynyluracil, 5-propynylcytosine, 5-methyl-cytosine, 5-bromocytosine, hypoxanthine, 2-amino-purine and 2,6-diaminopurine. Some of the base analogs enhanced third strand binding to the target duplex with one or other 'inverted' central base pair relative to the binding afforded by any of the canonical bases. Other analogs did the same for the duplexes with the 'direct' target pairs. The increasing order of triplex stabilization by these base analogs is: opposite the 'inverted' base pairs, for T.A, A < C < 5-pC < 5-pU < T < 5-BrC < 5-meC < 5-BrU < 2-AP < 2,6-DAP < Hy < G, for C.G, 2-AP < A < Hy < G < 5-pC < 5-BrC < 5-meC < C < 2,6-DAP < T < 5-BrU < 5-pU; opposite the 'direct' base pairs, for A.T, 2-AP < A < 5-meC < C < G < Hy < 2,6-DAP < 5-pU < T = 5-BrU < 5-BrC < 5-pC, for G.C, G < 2,6-DAP < 2-AP < A < Hy < T < 5-BrU < 5-pU < 5-pC < 5-BrC < C < 5-meC. (+info
Growth factor-regulated expression of enzymes involved in nucleotide biosynthesis: a novel mechanism of growth factor action.
Keratinocyte growth factor (KGF) is a potent and specific mitogen for epithelial cells, including the keratinocytes of the skin. We investigated the mechanisms of action of KGF by searching for genes which are regulated by this growth factor in cultured human keratinocytes. Using the differential display RT-PCR technology we identified the gene encoding adenylosuccinate lyase [EC 22.214.171.124] as a novel KGF-regulated gene. Adenylosuccinate lyase plays an important role in purine de novo synthesis. To gain further insight into the potential role of nucleotide biosynthesis in the mitogenic effect of KGF, we cloned cDNA fragments of the key regulatory enzymes involved in purine and pyrimidine metabolism (adenylosuccinate synthetase [EC 126.96.36.199], phosphoribosyl pyrophosphate synthetase [EC 188.8.131.52], amidophosphoribosyl transferase [EC 184.108.40.206], hypoxanthine guanine phosphoribosyl transferase [EC 220.127.116.11] and the multifunctional protein CAD which includes the enzymatic activities of carbamoyl-phosphate synthetase II [EC 18.104.22.168], aspartate transcarbamylase [EC 22.214.171.124] and dihydroorotase [EC 126.96.36.199]). Expression of all of these enzymes was upregulated after treatment with KGF and also with epidermal growth factor (EGF), indicating that these mitogens stimulate nucleotide production by induction of these enzymes. To determine a possible in vivo correlation between the expression of KGF, EGF and the enzymes mentioned above, we analysed the expression of the enzymes during cutaneous wound repair, where high levels of these mitogens are present. Indeed, we found a strong mRNA expression of all of these enzymes in the EGF- and KGF-responsive keratinocytes of the hyperproliferative epithelium at the wound edge, indicating that their expression might also be regulated by growth factors during wound healing. (+info
In vitro recycling of alpha-D-ribose 1-phosphate for the salvage of purine bases.
In this paper, we extend our previous observation on the mobilization of the ribose moiety from a purine nucleoside to a pyrimidine base, with subsequent pyrimidine nucleotides formation (Cappiello et al., Biochim. Biophys. Acta 1425 (1998) 273-281). The data show that, at least in vitro, also the reverse process is possible. In rat brain extracts, the activated ribose, stemming from uridine as ribose 1-phosphate, can be used to salvage adenine and hypoxanthine to their respective nucleotides. Since the salvage of purine bases is a 5-phosphoribosyl 1-pyrophosphate-dependent process, catalyzed by adenine phosphoribosyltransferase and hypoxanthine guanine phosphoribosyltransferase, our results imply that Rib-1P must be transformed into 5-phosphoribosyl 1-pyrophosphate, via the successive action of phosphopentomutase and 5-phosphoribosyl 1-pyrophosphate synthetase; and,in fact, no adenosine could be found as an intermediate when rat brain extracts were incubated with adenine, Rib-1P and ATP, showing that adenine salvage does not imply adenine ribosylation, followed by adenosine phosphorylation. Taken together with our previous results on the Rib-1P-dependent salvage of pyrimidine nucleotides, our results give a clear picture of the in vitro Rib-1P recycling, for both purine and pyrimidine salvage. (+info
Aliphatic analogues of nucleotides: synthesis and affinity towards nucleases.
DL-1-(2,3-Dihydroxypropyl)thymine was prepared by Hilbert-Johnson reaction of 2,4-dinethoxy-5-methylpyrimidine with allyl bromide followed by the osmium tetroxide catalyzed hydroxylation of the l-allyl-4-methoxy-5-methylpyrimidin-2-one obtained as an intermediate. The D-glycero enantiomer, R-1-(2,3-dihydroxypropyl)thymine and the corresponding 1-substituted uracil derivative were prepared from 3-O-p-toluenesulfonyl-1, 2-O-isopropylidene-D-glycerine and sodium salt of 4-methoxy-5-methylpyrimidin-2-one or 4-methoxypyrimidin-2-one followed by treatment with hydrogen chloride in ethanol. The phosphorylation of the above 2,3-dihydroxypropyl derivatives with phosphoryl chloride in triethyl phosphate afforded the corresponding 3-phosphates which were transformed into the 2',3'-cyclic phosphates by the condensation with N,N'-dicyclohexylcarbodiimide. The latter compounds of the D-glycero configuration are split by some microbial RNases to the 3-phosphates. (+info
Cleavage of the glycosidic linkage of pyrimidine ribonucleosides by the bisulfite-oxygen system.
When a solution containing 2 mM uridine, 20 mM sodium bisulfite, 0.1 mM MnCl(2), and 100 mM sodium phosphate buffer of pH 7.0 was incubated aerobically at 37 degrees or 0 degrees , partial cleavage of the glycosidic linkage of uridine took place. About 20% of the uridine was converted to uracil by the incubation for 4 hrs. Cytosine was produced from cytidine by similar treatment with bisulfite. These reactions were caused by free radicals generated by Mn(2+)-catalyzed autoxidation of bisulfite. Glycosidic bond cleavage by the bisulfite-oxygen system was not detected for adenosine, AMP, guanosine, GMP, thymidine, TMP, deoxyuridine, dCMP, dAMP, and dGMP. When poly(U) and poly(C) were treated with 20 mM sodium bisulfite in the same manner, chain fission of the polymer occurred as judged by the elution-pattern change in gel filtration through Sephadex columns. No change in the elution pattern was observed for bisulfite-treated poly(A), poly(U). poly(A) or tRNA. (+info