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PubMed1989

[Ligase joining of oligodeoxynucleotides on a oligodeoxynucleotide analog matrix containing P-S-C(5')-internucleotide bonds].

Joining of oligodeoxynucleotides by T4 polynucleotide ligase on an oligodeoxynucleotide template analogue having P--S--C(5') internucleotide bonds was investigated. The enzyme did ligate the oligodeoxynucleotides but with an extremely low rate. The major product of the enzymatic reaction proved to be the adenylylated intermediate of the 5'-phosphorylated oligodeoxynucleotide, the product of the second stage of the overall ligation reaction. It is noteworthy that this intermediate is not accumulated in ligase reactions under standard conditions when DNA templates rather than template analogues were used.

Chemical Phenomena↗

PubMed1977

Bacteriophage T4 RNA ligase. Reaction intermediates and interaction of substrates.

Bacteriophage T4 RNA ligase catalyzes the ATP-dependent ligation of a 5'-phosphoryl-terminated nucleic acid donor to a 3'-hydroxyl-terminated nucleic acid acceptor. We have identified adenylylated DNA and RNA reaction intermediates in which the AMP moiety is attached by a pyrophosphate bond to the 5'-phosphoryl group of the donor. A large amount of DNA-adenylate accumulates during the reaction and the dependence of joining and adenylylation on chain length are similar. The adenylylated donor is joined by ligase to an acceptor in the absence of ATP, and AMP is released stoichiometrically in this reaction. The acceptor is not only a substrate in the reaction but also a cofactor for adenylylation of the donor; in the absence of a 3'-hydroxyl group the activated intermediate does not form. The activated DNA need not join to the acceptor that initially stimulated activation but can also join to another acceptor. This process of acceptor exchanges has proven useful for promoting the cyclization of small DNA substrates and the synthesis of DNA co-polymers.

Coliphages↗

PubMed1995

The accessibility of thiophosphorylated groups in DNA fragments to the enzymatic activity of ligases and restriction endonuclease Bbs I.

The aim of this paper was to test the possibility to ligate and hydrolyse DNA sequences containing thiomodified ends and bonds. T4 DNA ligase was shown to ligate DNA fragments regardless of whether it contains phosphorylated or thiophosphorylated 5'-end. But the cleavage of an internally thiomodified phosphodiester bond was found to be totally inhibited when using the non-palindromic restrictase Bbs I. The special properties of this restriction endonuclease should allow the development of an oriented cloning strategy when combined with T4 ligase and a thiophosphorylation of DNA fragments.

Base Sequence↗

PubMed1995

[Study of the substrate specificity of T4 RNA ligase: interaction of the enzyme with ATP analogs modified through the ribose residue and with affinity sorbents].

To elucidate the role of the ribose moiety in substrate binding, various ATP derivatives modified in ribose moiety were studied as probes for the T4 RNA ligase first stage reaction. The kinetic parameters for competitive inhibition were determined. Inhibition experiments using substrate analogs demonstrated that the major binding determinants of ATP analogs were purine and triphosphate moieties of ATP; modification of the ribose moiety was not critical. Adenosine triphosphates attached to agarose were used as affinity adsorbent for purification of T4 RNA ligase. These derivatives had been successfully used in reversible binding of the enzyme. Best results were achieved with agarose coupled via N6 of the purine moiety of ATP.

Adenosine Triphosphate↗

PubMed1993

[Ligase chain reaction (LCR)].

Ligase chain reaction (LCR) is a ligation-mediated amplification technique of a target DNA sequence using oligonucleotides and thermostable ligase. LCR is useful for the detection of known DNA sequences and point mutations in a limited amount of DNA. We introduce the principle, development, and protocol of this simple and convenient technique for DNA analysis.

Base Sequence↗

PubMed1993

Simultaneous mutagenesis of multiple sites: application of the ligase chain reaction using PCR products instead of oligonucleotides.

A method is described for preparing mutants with multiple, site-directed mutations by ordered coupling of PCR-generated fragments catalyzed by a thermostable DNA ligase. Annealing of the sense strands of the fragments to a single-stranded (antisense) template created a full-length sense strand leaving only nicks that were closed by ligation. Mutations were introduced in the PCR primers. Following 40 cycles of denaturation and annealing, tags on the flanking primers of the ligase chain reaction product were used specifically to amplify the mutated product with specific primers that could not amplify the original template. The amplified ligation product was cloned and was found to contain the desired restriction sites introduced by way of the mutagenic primers.

Bacillus↗

PubMed1999

Components of an SCF ubiquitin ligase localize to the centrosome and regulate the centrosome duplication cycle.

Centrosomes organize the mitotic spindle to ensure accurate segregation of the chromosomes in mitosis. The mechanism that ensures accurate duplication and separation of the centrosomes underlies the fidelity of chromosome segregation, but remains unknown. In Saccharomyces cerevisiae, entry into S phase and separation of spindle pole bodies each require CDC4 and CDC34, which encode components of an SCF (Skp1-cullin-F-box) ubiquitin ligase, but a direct (SCF) connection to the spindle pole body is unknown. Using immunofluorescence microscopy, we show that in mammalian cells the Skp1 protein and the cullin Cul1 are localized to interphase and mitotic centrosomes and to the cytoplasm and nucleus. Deconvolution and immunoelectron microscopy suggest that Skp1 forms an extended pericentriolar structure that may function to organize the centrosome. Purified centrosomes also contain Skp1, and Cul1 modified by the ubiquitin-like molecule NEDD8, suggesting a role for NEDD8 in targeting. Using an in vitro assay for centriole separation in Xenopus extracts, antibodies to Skp1 or Cul1 block separation. Proteasome inhibitors block both centriole separation in vitro and centrosome duplication in Xenopus embryos. We identify candidate centrosomal F-box proteins, suggesting that distinct SCF complexes may direct proteolysis of factors mediating multiple steps in the centrosome cycle.

3T3 Cells↗

PubMed1987

The 5'-O-phosphonomethyl analog of ATP. Studies of substrate properties in ligase-dependent reactions.

The 5-O-phosphonomethyl analog of ATP (ATPc) and its interaction with different enzymes, catalysing synthesis of C-O-, C-S-, C-N- and C-C-bond were investigated. It was shown ATPc to have substrate properties and to be involved in all studied ligase-dependent reactions. Kinetic parameters of the interaction of alternative substrate - ATPc with all studied enzymes were established and the comparison of ATPc with other phosphonate analogs of ATP was performed.

Acetyl-CoA Carboxylase↗

PubMed2004

Low expression of human tubulin tyrosine ligase and suppressed tubulin tyrosination/detyrosination cycle are associated with impaired neuronal differentiation in neuroblastomas with poor prognosis.

Neuroblastoma (NBL), one of the most common childhood solid tumors, has a distinct nature in different prognostic subgroups. However, the precise mechanism underlying this phenomenon remains largely unknown. To understand the molecular and genetic bases of neuroblastoma, we have generated its cDNA libraries and identified a human ortholog of tubulin tyrosine ligase gene (hTTL/Nbla0660) as a differentially expressed gene at high levels in a favorable subset of the tumor. Tubulin is subjected to several types of evolutionarily conserved posttranslational modification, including tyrosination and detyrosination. Tubulin tyrosine ligase catalyzes ligation of the tyrosine residue to the COOH terminus of the detyrosinated form of alpha-tubulin. The measurement of hTTL mRNA expression in 74 primary neuroblastomas by quantitative real-time reverse transcription-PCR revealed that its high expression was significantly associated with favorable stages (1, 2 and 4s; p = 0.0069), high TrkA expression (p = 0.002), a single copy of MYCN (p < 0.00005), tumors found by mass screening (p = 0.0042), nonadrenal origin (p = 0.0042) and good prognosis (p = 0.023). The log-rank test showed that high expression of hTTL was an indicator of favorable prognosis (p = 0.026). Immunohistochemical analysis using specific antibodies generated by us demonstrated that tyrosinated tubulin (Tyr-tubulin), detyrosinated tubulin (Glu-tubulin) and hTTL as well as Delta2-tubulin were positive in favorable tumors, whereas only Delta2-tubulin was positive in the tumors with MYCN amplification. In an RTBM1 neuroblastoma cell line, hTTL was increased after treating the cells with bone morphogenetic protein 2 (BMP2) or all-trans retinoic acid (RA), which induced neuronal differentiation. These results suggest that the deregulated tubulin tyrosination/detyrosination cycle caused by decreased expression of hTTL is associated with inhibition of neuronal differentiation and enhancement of cell growth in the primary neuroblastomas with poor outcome.

Amino Acid Sequence↗

PubMed1996

Kinetic and crystallographic studies of Escherichia coli UDP-N-acetylmuramate:L-alanine ligase.

Uridine diphosphate-N-acetylmuramate:L-alanine ligase (EC 6.3.2.8, UNAM:L-Ala ligase or MurC gene product) catalyzes the ATP-dependent ligation of the first amino acid to the sugar moiety of the peptidoglycan precursor. This is an essential step in cell wall biosynthesis for both gram-positive and gram-negative bacteria. Optimal assay conditions for initial velocity studies have been established. Steady-state assays were carried out to determine the effect of various parameters on enzyme activity. Factors studies included: cation specificity, ionic strength, buffer composition and pH. At 37 degrees C and pH 8.0, kcat was equal to 980 +/- 40 min-1, while K(m) values for ATP, UNAM, and L-alanine were, 130 +/- 10, 44 +/- 3, and 48 +/- 6 microM, respectively. Of the metals tested only Mn, Mg, and Co were able to support activity. Sodium chloride, potassium chloride, ammonium chloride, and ammonium sulfate had no effect on activity up to 75 mM levels. The enzyme, in appropriate buffer, was stable enough to be assayed over the pH range of 5.6 to 10.1. pH profiles of Vmax/K(m) for the three substrates and of Vmax were obtained. Crystallization experiments with the enzyme produced two crystal forms. One of these has been characterized by X-ray diffraction as monoclinic, space group C2, with cell dimensions a = 189.6, b = 92.1, c = 75.2 A, beta = 105 degrees, and two 54 kDa molecules per asymmetric unit. It was discovered that the enzyme will hydrolyze ATP in the absence of L-alanine. This L-alanine independent activity is dependent upon the concentrations of both ATP and UNAM; kcat for this activity is less than 4% of the biosynthetic activity measured in the presence of saturating levels of L-alanine. Numerous L-alanine analogs tested were shown to stimulate ATP hydrolysis. A number of these L-alanine analogs produced novel products as accessed by HPLC and mass spectral analysis. All of the L-alanine analogs tested as inhibitors were competitive versus L-alanine.

Crystallization↗

PubMed1977

On the specificity of the uridine diphospho-N-acetylmuramyl-alanyl-D-glutamic acid: diamino acid ligase of Bifidobacterium globosum.

The peptidoglycan of Bifidobacterium globosum contains ornithine and lysine alternately in the same position of the peptide subunit. The uridine diphospho-N-acetylmuramyl-alanyl-D-glutamic acid: diamino acid ligase of this organism was purified 700-fold. Since the activities for the incorporation of ornithine and lysine into uridine diphospho-N-acetylmuramyl-tripeptide did not separate during purification and since the incorporation of ornithine is competitively inhibited by lysine and vice versa, both ornithine and lysine are assumed to be incorporated by one single enzyme. Studies on the specificity of the ligase toward analogs of ornithine have shown that the enzyme requires a diamino, monocarboxylic acid with 4-6 carbon atoms. Methylation of the epsilon-amino group or hydroxylation of the delta-carbon atom of lysine decreases the competitive properties of the analog, whereas the substitution of the gamma-methylen group by sulfur (S-2-aminoethyl cysteine) results in a highly competitive compound.

Actinomycetaceae↗

PubMed1997

Cloning and characterization of the lipoyl-protein ligase gene LIPB from the yeast Kluyveromyces lactis: synergistic respiratory deficiency due to mutations in LIPB and mitochondrial F1-ATPase subunits.

The mgi1-4 and mgi2-1 mutants of the petite-negative yeast Kluyveromyces lactis have mutations in the beta- and alpha-subunits of the mitochondrial F1-ATPase, respectively. The mutants are respiratory competent but can form petites with deletions in mitochondrial DNA. In this study a cryptic nuclear mutation (lipB-1) was identified which, in combination with the mgi alleles, displays a synergistic respiratory-deficient phenotype on glycerol medium. The gene defined by the mutation was cloned and shown to encode a polypeptide of 332 amino acids with an N-terminal sequence characteristic of a mitochondrial targeting signal. The deduced protein shares 27% sequence identity with the product of the Escherichia coli lipB gene, which encodes a lipoyl-protein ligase involved in the attachment of lipoyl groups to lipoate-dependent apoproteins. A K. lactis strain carrying a disrupted lipB allele is severely compromised for growth on glycerol medium. The growth defect cannot be rescued by addition of lipoic acid, but cell growth can be restored on medium containing ethanol plus succinate. In addition, it was observed that lipB mutants of K. lactis, unlike the wild-type, are unable to utilize glycine as sole nitrogen source, indicating that activity of the glycine decarboxylase complex (GDC) is also affected. Taken together, these findings suggest that LIPB is the main determinant of the lipoyl-protein ligase activity required for lipoylation of enzymes such as alpha-ketoacid dehydrogenases and GDC.

Amino Acid Sequence↗

PubMed1990

3-azido-L-tyrosine as a photoinhibitor of tubulin:tyrosine ligase. Role of thiol groups.

We have synthesized the photoactivatable probes 3-azido-L-tyrosine and p-azido-L-phenylalanine and studied their capacity to inhibit the incorporation of [3H]tyrosine into tubulin catalyzed by tubulin:tyrosine ligase. Without illumination, only 3-azido-L-tyrosine reversibly inhibits the enzyme. Upon illumination, both reagents irreversibly photoinactivate the enzyme in a similar way. The ligase can be protected against photoinactivation by reversibly blocking essential thiol groups with pCMB during illumination.

Affinity Labels↗

PubMed1994

Sequence of the vanB and ddl genes encoding D-alanine:D-lactate and D-alanine:D-alanine ligases in vancomycin-resistant Enterococcus faecalis V583.

A pair of degenerate oligodeoxyribonucleotides was used to amplify, by the polymerase chain reaction (PCR), DNA fragments internal to genes encoding D-Ala:D-Ala ligase-related proteins of vancomycin-resistant (VmR) Enterococcus faecalis V583. Cloning and nucleotide sequencing of the PCR products indicated that fragments of two genes, designated vanB and ddl, were co-amplified. The vanB gene was previously shown to be present in Enterococcus strains expressing VanB-type VmR [Quintiliani Jr. et al., J. Infect. Dis. 8 (1993) 943-950]. The ddl gene was detected by Southern hybridization in all VmR and VmS strains of En. faecalis, but not in representatives of 17 other species of Enterococcus. The vanB and ddl genes were cloned in bacteriophage lambda and sequenced. There was extensive similarity (76% amino-acid identity) between the product of vanB and the VmR protein, VanA. The product of ddl, the D-Ala:D-Ala ligases, DdlA and DdlB, of Escherichia coli and the resistance proteins, VanA and VanB, were more distantly related (32-40% aa identity). After induction of VmR, En. faecalis V583 synthesized the cell wall precursor, UDP-N-acetylmuramyl-tetrapeptide-D-lactate, indicating that the mechanism of glycopeptide resistance in strains with the VanA and VanB phenotype is similar.

Amino Acid Sequence↗

PubMed2005

Thermodynamic properties of oxidoreductase, transferase, hydrolase, and ligase reactions.

Transferases formally couple together two oxidoreductase reactions or two hydrolase reactions. Therefore the thermodynamic properties of transferase reactions can be calculated from differences between thermodynamic properties of two oxidoreductase or two hydrolase reactions. Ligases couple together two hydrolase reactions, and so their thermodynamic properties can be calculated from differences between two hydrolase reactions. These relationships are demonstrated by calculating standard transformed Gibbs energies of reaction and the changes in binding of hydrogen ions at pHs 5-9 of a number of oxidoreductase, transferase, hydrolase, and ligase reactions by use of the data base BasicBiochemData2 and its recent extensions. Coupling is not restricted to two reactions, and an example is given of the coupling of three reactions.

Hydrogen-Ion Concentration↗

PubMed2004

8-OxoG retards the activity of the ligase III/XRCC1 complex during the repair of a single-strand break, when present within a clustered DNA damage site.

Ionising radiation produces clustered DNA damage. Recent studies have established that the efficiency of excision of a lesion within clustered damage sites is reduced. This study presents evidence that the repair of clustered DNA damage is compromised, relative to that of the isolated lesions, since the lifetime of both lesions is extended by up to eight fold. Simple clustered damage sites, comprised of a single-strand break, one or five bases 3' or 5' to 8-oxoG on the opposite strand, were synthesised in oligonucleotides and repair carried out in XRS5 nuclear extracts. The rate of repair of the single-strand break within these clustered damage sites is reduced, mainly due to inhibition of the DNA ligase III/XRCC1 complex. The single-strand break, present as an isolated lesion, is repaired by short-patch base excision repair, however the mechanism of repair of the single-strand break within the clustered damage site is asymmetric. When the lesions are 5' to each other, the single-strand break is rejoined by short-patch repair whereas the rejoining of the single-strand break occurs by long-patch type repair when the lesions are 3' to one another. The retardation of DNA ligase III/XRCC1 complex, following addition of one base, is responsible for the initiation of long-patch base excision repair when the lesions are 3' to each other. The lesions within the cluster are processed sequentially, the single-strand break being repaired before excision of 8-oxoG, limiting the formation of double-strand breaks to <2%. Stalled processing of clustered DNA damage is suggested to have implications for mutation induction by radiation.

DNA Damage↗

PubMed2004

Regulation of cullin-based ubiquitin ligases by the Nedd8/RUB ubiquitin-like proteins.

The expression of the ubiquitin related protein Nedd8/RUB is essential for growth in most organisms. Nedd8/RUB has been shown to modify the cullin subunit of culling-based ubiquitin protein ligases (E3). Neddylation acts to regulate the function of these E3s and organisms with lesions in the neddylation process exhibit severe growth defects. In this review we describe the proteins that participate in neddylation and discuss a model for Nedd8/RUB regulation of ubiquitin ligase function.

Animals↗

PubMed2003

Mammalian Numb is a target protein of Mdm2, ubiquitin ligase.

Drosophila Numb protein functions as an antagonist against Notch signal. The expression of this protein is asymmetrical in divided cells and thought to be involved in the neural cell differentiation and/or cell fate. Human homologue of Numb (hNumb) was cloned as Mdm2-binding protein by yeast two-hybrid screening. Since Mdm2 is an oncoprotein and has ubiquitin ligase activity toward tumor suppressor p53, we assessed to find out whether Mdm2 ubiquitinylates the hNumb protein. The recombinant hNumb expressed in Sf-9 cells using baculovirus protein expression system bound to Mdm2 in vitro. When hNumb was subjected to in vitro ubiquitinylation assay system, which contains E1, E2, or UbcH5c, and Mdm2, hNumb was ubiquitinylated as efficiently as the p53 protein. However, when the Ring-finger domain mutant of Mdm2 was used in place of wild-type Mdm2, hNumb was not ubiquitinylated. Furthermore, when U2OS cells were co-transfected with hNumb and Mdm2, the hNumb protein was ubiquitinylated and degraded. These data strongly suggest that Mdm2 functions as the ubiquitin ligase toward hNumb and that it induces its degradation in intact cells.

Animals↗