Poly(ADP-ribose) polymerase forms loops with DNA

The interaction between highly purified poly(ADP-ribose) polymerase from calf thymus and different topological forms of pBR322 DNA has been studied by gel retardation electrophoresis and electron microscopy. We show that: (i) in the absence of nicks on DNA the enzyme has a marked affinity for supercoiled (form I) DNA, (ii) in the presence of single stranded breaks poly(ADP-ribose) polymerase preferentially binds to form II, (iii) in all cases enzyme molecules are frequently located at DNA intersections, (iv) a cooperative binding of the enzyme on DNA occurs.     

Poly(ADP-ribose) polymerase: molecular biological aspects.

A number of roles have been ascribed to poly(ADP-ribose) polymerase* including involvement in DNA repair, cell proliferation, differentiation and transformation. Cloning of the gene has allowed the development of molecular biological approaches to elucidate the structure and the function(s) of this highly conserved enzyme. This article will review the recent results obtained in this field.     

Poly(ADP-ribose)polymerase: a novel finger protein.

By Energy Dispersive X-ray fluorescence we have determined that calf thymus poly(ADP-ribose) polymerase binds two zinc ions per enzyme molecule. Using 65Zn (II) for detection of zinc binding proteins and polypeptides on western blots, we found that the zinc binding sites are localized in a 29 kd N-terminal fragment which is included in the DNA binding domain. Metal depletion and restoration experiments proved that zinc is essential for the binding of this fragment to DNA as tested by Southwestern assay. These results correlate with the existence of two putative zinc finger motifs present in the N-terminal part of the human enzyme. Poly(ADP-ribose)polymerase fingers could be involved in the recognition of DNA strand breaks and therefore in enzyme activation.     

Poly(ADP-ribose)polymerase: a perplexing participant in cellular responses to DNA breakage

Poly(ADP-ribose) polymerase is a major nuclear protein of 116 kd, coded by a gene on chromosome 1, that plays a role in cellular responses to DNA breakage. The polymerase binds to DNA at single- and double-strand breaks and synthesizes long branched chains of poly(ADP-ribose), which covalently, but transiently, modifies itself and numerous other cellular proteins and depletes cells of NAD+. This much is known, but the physiological role of the polymerization-degradation cycle is still unclear. Poly(ADP-ribosyl)ation of proteins generally inhibits their function and can dissociated chromatin proteins from DNA. Inhibition of poly(ADP-ribose) polymerase increases to toxicity of alkylating agents and some other DNA-damaging agents and increases sister-chromatid exchange frequencies. During repair of alkylation damage, inhibition of poly(ADP-ribose) polymerase makes no change in excision of damaged products. increases the total number of repair patches, accelerates the rejoining of DNA breaks, and makes variable increases or decreases in net break frequencies. The polymerization cycle consequently is a major player in the response of cells to DNA breakage, but the game it plays is yet to be explained.     

Poly(ADP-ribose) polymerase inhibits DNA synthesis initiation in the absence of NAD

Poly(ADP-ribose) polymerase (ADPRP) is a nuclear enzyme that transfers ADP-ribose from NAD+ to diverse nuclear proteins. Previously, the function of ADPRP was considered to relate exclusively to its catalytic activity. However, recent experiments have shown that ADPRP is actually an abundant DNA-binding protein, and that the potential catalytic activity of the enzyme is more than 100-fold greater than the measured rates of NAD+ turnover in intact cells. To better understand the role of ADPRP, we have used highly purified ADPRP and a monospecific autoantibody to examine the effects of ADPRP on in vitro DNA synthesis in the presence or absence of NAD+ substrate. The data show that DNA synthesis initiation is blocked by ADPRP and that auto-poly (ADP-ribosyl)ation reverses the process by diminishing the DNA binding capacity of the protein. These results suggest that ADPRP actually is a structural DNA binding protein, whose catalytic activity serves to modulate its interaction with DNA.     

Poly(ADP-ribose) polymerase activity in mouse cells which exhibit temperature-sensitive DNA synthesis

The poly(ADP-ribose) polymerase activity of wild-type mouse L cells and of Balb/C-3T3 mouse fibroblasts remained relatively unchanged (at approx. 400 nmol substrate utilized/mg DNA per h) in actively-growing cells incubated at 34 degrees C or at 38.5 degrees C for at least 72 h. A similar result was obtained with the following temperature-sensitive cells grown at the permissive temperature (34 degrees C): ts A1S9 mouse L cells, ts C1 mouse L cells and Balb/C-3T3 ts mouse fibroblasts. The poly(ADP-ribose) polymerase activity of the temperature-sensitive cells was little affected during incubation for 20-24 h at the non-permissive temperature of 38.5 degrees C under which conditions temperature-inactivation of DNA replication was complete. Thereafter, this enzyme activity was found to increase some 2-fold, at a time when normal semi-conservative DNA synthesis was totally suppressed and replaced by repair replication (Sheinin, R. and Guttman, S. (1977) Biochim. Biophys. Acta 479, 105-118; Sheinin, R., Dardick, I. and Doane, F.W. (1980) Exp. Cell. Res., in the press).     

Poly(ADP-ribose) polymerase 1 accelerates single-strand break repair in concert with poly(ADP-ribose) glycohydrolase

Single-strand breaks are the commonest lesions arising in cells, and defects in their repair are implicated in neurodegenerative disease. One of the earliest events during single-strand break repair (SSBR) is the rapid synthesis of poly(ADP-ribose) (PAR) by poly(ADP-ribose) polymerase (PARP), followed by its rapid degradation by poly(ADP-ribose) glycohydrolase (PARG). While the synthesis of poly(ADP-ribose) is important for rapid rates of chromosomal SSBR, the relative importance of poly(ADP-ribose) polymerase 1 (PARP-1) and PARP-2 and of the subsequent degradation of PAR by PARG is unclear. Here we have quantified SSBR rates in human A549 cells depleted of PARP-1, PARP-2, and PARG, both separately and in combination. We report that whereas PARP-1 is critical for rapid global rates of SSBR in human A549 cells, depletion of PARP-2 has only a minor impact, even in the presence of depleted levels of PARP-1. Moreover, we identify PARG as a novel and critical component of SSBR that accelerates this process in concert with PARP-1.     

Poly(ADP-ribose) polymerase (PARP-1) is not involved in DNA double-strand break recovery

Background  

The cytotoxicity and the rejoining of DNA double-strand breaks induced by γ-rays, H₂O₂ and neocarzinostatin, were investigated in normal and PARP-1 knockout mouse 3T3 fibroblasts to determine the role of poly(ADP-ribose) polymerase (PARP-1) in DNA double-strand break repair.     

Poly(ADP-ribose) polymerase localizes to the centrosomes and chromosomes

Poly(ADP-ribose) polymerase (PARP) takes part mainly in regulation of DNA repair, thereby maintaining genomic stability in the nucleus. However, what role PARP plays in mitotic cells is not known. Centrosomes play an important role in maintaining the fidelity of chromosome distribution during cell division. Loss of these functions might cause chromosomal instability and aneuploidy. p53 and BRCA1 were recently found to localize to the centrosome at mitosis. We found that PARP is localized to the centrosomes and the chromosomes at cell-division phase and interphase by indirect immunofluorescence. Furthermore, by analysis of isolated centrosomes PARP protein was found to associate with the centrosomes during mitosis. These data suggest that PARP may be involved in maintenance of chromosomal stability.     

聚腺苷二磷酸核糖基聚合酶──在DNA损伤修复及程序性死亡中的作用

聚腺苷二磷酸核糖基聚合酶(poly (ADP-ribose) polyerase, PARP)是存在于多数真核细胞中的一个蛋白质翻译后修饰酶,它可催化组蛋白H₁等重要核蛋白及它自身的聚腺苷二磷酸核糖基化作用.细胞受到外界损伤因子作用时, DNA发生链断裂,PARP结合到DNA断裂口,其催化活性被激活,修饰受体蛋白,进而引发一系列级联反应.这种性质使PARP有可能作为细胞内的分子感受器和传感器,启动细胞内对损伤作出反应的信号传导机制,从而根据细胞受损程度决定细胞的命运：修复或是死亡．     

Poly(ADP-ribose) polymerase from Ehrlich ascites tumor cells. Properties of the purified polymerase.

Poly(ADP-ribose) polymerase from Ehrlich ascites tumor cells, partially purified by chromatography on DNA-agarose, was obtained as a more than 80% homogeneous preparation by isoelectric focusing in a sucrose gradient. The polymerase activity was shown to be associated with the major protein in the preparation. Results obtained by electrophoresis in the presence of sodium dodecyl-sulfate indicated that poly(ADP-ribose) polymerase consists of a polypeptide chain with a molecular weight of 130 000. Ultracentrifugation at non-denaturating conditions indicated that the active enzyme may be an oligomeric form of this polypeptide chain. The isoelectric point of the polymerase was 9.40. The effects of various additions to the assay mixture on the synthesis of poly(ADP-ribose) as well as some kinetic data, are given. It is shown that poly(ADP-ribose) is a highly efficient inhibitor of its own synthesis, and results are presented which suggest that the well-known stimulatory effect of DNA on the synthesis is due to reduction of this inhibitory effect of the product.     

Poly(ADP-ribose) polymerase: A guardian of the genome that facilitates DNA repair by protecting against DNA recombination

We have studied the clonogenic survival response to X-rays and MNNG of V79 Chinese hamster cells and two derivative cell lines, ADPRT54 and ADPRT351, deficient in poly(ADP-ribose) polymerase (PARP) activity. Under conditions of exponential growth, both PARP-deficient cell lines are hypersensitive to X-rays and MNNG compared to their parental V79 cells. In contrast, under growth-arrested, confluent conditions, V79 and PARP-deficient cells become similarly sensitive to X-rays and MNNG suggesting that PARP may be involved in the repair of X-ray or MNNG-induced DNA damage in logarithmically growing cells but not in growth-arrested confluent cells. This suggestion, however, creates a dilemma as to how PARP can be involved in DNA repair in only selected growth phases while it is functionally active in all growth phases. To explain these paradoxical results and resolve this dilemma we propose a hypothesis based on the consistent observation that inhibition of PARP results in a significant increase in sister chromatid exchange (SCEs). Thus, we propose that PARP is a guardian of the genome that protects against DNA recombination. We have extended this theme to provide an explanation for our results and the studies done by many others.     

DNA polymerase beta -mediated long patch base excision repair. Poly(ADP-ribose)polymerase-1 stimulates strand displacement DNA synthesis.

Recently, photoaffinity labeling experiments with mouse cell extracts suggested that PARP-1 functions as a surveillance protein for a stalled BER intermediate. To further understand the role of PARP-1 in BER, we examined the DNA synthesis and flap excision steps in long patch BER using a reconstituted system containing a 34-base pair BER substrate and five purified human enzymes: uracil-DNA glycosylase, apurinic/apyrimidinic endonuclease, DNA polymerase beta, flap endonuclease-1 (FEN-1), and PARP-1. PARP-1 stimulates strand displacement DNA synthesis by DNA polymerase beta in this system; this stimulation is dependent on the presence of FEN-1. PARP-1 and FEN-1, therefore, cooperate to activate long patch BER. The results are discussed in the context of a model for BER sub-pathway choice, illustrating a dual role for PARP-1 as a surveillance protein for a stalled BER intermediate and an activating factor for long patch BER DNA synthesis.