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Query: EC:2.7.7.7 (DNA polymerase)
 17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Sites of replication in synchronized HeLa cells were visualized by light and electron microscopy; cells were permeabilized and incubated with biotin-16-dUTP, and incorporation sites were immunolabelled. Electron microscopy of thick resinless sections from which approximately 90% chromatin had been removed showed that most DNA synthesis occurs in specific dense structures (replication factories) attached to a diffuse nucleoskeleton. These factories appear at the end of G1-phase and quickly become active; as S-phase progresses, they increase in size and decrease in number like sites of incorporation seen by light microscopy. Electron microscopy of conventional thin sections proved that these factories are a subset of nuclear bodies; they changed in the same characteristic way and contained DNA polymerase alpha and proliferating cell nuclear antigen. As replication factories can be observed and labelled in non-permeabilized cells, they cannot be aggregation artifacts. Some replication occurs outside factories at discrete sites on the diffuse skeleton; it becomes significant by mid S-phase and later becomes concentrated beneath the lamina.
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PMID:Replication factories and nuclear bodies: the ultrastructural characterization of replication sites during the cell cycle. 798 77

The crystal structure of the processivity factor required by eukaryotic DNA polymerase delta, proliferating cell nuclear antigen (PCNA) from S. cerevisiae, has been determined at 2.3 A resolution. Three PCNA molecules, each containing two topologically identical domains, are tightly associated to form a closed ring. The dimensions and electrostatic properties of the ring suggest that PCNA encircles duplex DNA, providing a DNA-bound platform for the attachment of the polymerase. The trimeric PCNA ring is strikingly similar to the dimeric ring formed by the beta subunit (processivity factor) of E. coli DNA polymerase III holoenzyme, with which it shares no significant sequence identity. This structural correspondence further substantiates the mechanistic connection between eukaryotic and prokaryotic DNA replication that has been suggested on biochemical grounds.
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PMID:Crystal structure of the eukaryotic DNA polymerase processivity factor PCNA. 800 Nov 57

The in vitro replication of DNA containing the bovine papillomavirus (BPV-1) origin has been carried out with cell-free extracts from mouse FM3A and human HeLa cells. DNA synthesis required the E1 protein, the minimal origin of replication (nucleotides 7911-22 of the BPV-1 genome), and, at low levels of FM3A extract, the addition of the human single-stranded DNA-binding protein (also called RP-A or RF-A). The E2 protein was not absolutely required, but could stimulate DNA synthesis at low levels of E1. DNA synthesis was also reconstituted using purified proteins from HeLa cells. These protein factors included human single-stranded DNA-binding protein, topoisomerase I, and DNA polymerase (pol) alpha-primase complex. At low concentrations of pol alpha-primase complex, the formation of high molecular weight products was dependent on the addition of DNA polymerase delta holoenzyme containing proliferating cell nuclear antigen and activator 1, also called RF-C. We have overexpressed and isolated the E1 protein from bacteria. This protein also supported BPV DNA synthesis, both in crude extracts and with purified proteins suggesting that E1 phosphorylation is not required for BPV DNA replication in vitro.
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PMID:Replication of bovine papillomavirus type 1 origin-containing DNA in crude extracts and with purified proteins. 800 13

DNA polymerases (pol) alpha, delta and epsilon of a mouse cell line FM3A and its temperature-sensitive derivative tsFT20, which is defective in DNA replication at a non-permissive temperature, were purified by chromatographic procedures monitored by a set of relatively specific assays for the respective DNA polymerase activities. The pol epsilon activity was separated into two fractions with similar enzymatic properties except for their optimal KCl concentrations and processivities. The fractions of pol delta and epsilon were not homogeneous, but their identities were confirmed by their sensitivities to DNA polymerase inhibitors, their associated 3'-->5' exonuclease activities, optimal concentrations of salts, dependencies on the proliferating cell nuclear antigen and processivities in polymerization, which also excluded significant contamination with other DNA polymerases. Of the DNA polymerases prepared from tsFT20 cells, only pol alpha showed greatly decreased activity and remarkable sensitivity to the non-permissive temperature, demonstrating that pol delta and epsilon, the other polymerases supposed to be involved in nuclear DNA replication, are unequivocally different entities from pol alpha. The level of pol epsilon activity tsFT20 was also significantly lower than in the parental cells, suggesting cooperation and/or interaction between pol alpha and epsilon, and some relevance of pol epsilon to DNA replication.
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PMID:Comparison of DNA polymerases alpha, delta, and epsilon of mouse cell line FM3A and its temperature-sensitive mutant tsFT20. 803 23

We have defined a coordinate program of transcription of S-phase genes (DNA polymerase alpha, PCNA and the two ribonucleotide reductase subunits) that can be induced by the G1 cyclin, cyclin E. In Drosophila embryos, this program drives an intricate spatial and temporal pattern of gene expression that perfectly parallels the embryonic program of S-phase control. This dynamic pattern of expression is not disrupted by a mutation, string, that blocks the cell cycle. Thus, the transcriptional program is not a secondary consequence of cell cycle progression. We suggest that developmental signals control this transcriptional program and that its activation either directly or indirectly drives transition from G1 to S phase in the stereotyped embryonic pattern.
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PMID:Developmental control of a G1-S transcriptional program in Drosophila. 805 Mar 59

Upstream regions containing a novel common 8-base pair (bp) palindromic sequence, 5'-TATCGATA (Drosophila DNA replication-related element (DRE)), are required for the high expression of Drosophila genes for DNA polymerase alpha and the proliferating cell nuclear antigen (PCNA) (an auxiliary protein for DNA polymerase delta). Three DREs and one DRE are present in the DNA polymerase alpha gene (nucleotides-217, -83, and -30 with respect to the transcription initiation site) and in the PCNA gene (nucleotide-100), respectively. Deletions or 2-bp insertional mutations of DRE sequences led to an extensive reduction of promoter activities of both genes. Chemically synthesized oligonucleotides containing DRE sequences greatly stimulated the activity of the heterologous promoter of the Drosophila metallothionein gene, in addition to the promoter of the PCNA gene, when they were placed upstream from these promoters in a normal or a reverse orientation. The stimulatory effect increased synergistically and depended on the number of DREs. DRE activated the promoter when placed within 1.4 kilobases upstream from the promoter, but was much less active when placed 2.5 kilobases or more apart from the promoter. Using a gel mobility shift assay method, we obtained evidence for a protein factor (DREF) in the nuclear extract of cultured Drosophila cells (Kc cells), and this factor specifically binds to DREs of both genes. DNase I footprinting analysis indicated that DREF binds to the 24-bp DRE region of the DNA polymerase alpha gene in which 8-bp palindromic sequences are centered. A UV cross-linking experiment revealed that a polypeptide of approximately 90 kDa in the nuclear extract interacts directly with the DRE sequence. Using DRE-conjugated latex particles, DREF was affinity-purified from the Kc cell nuclear extract. By comparing results obtained by SDS-polyacrylamide gel electrophoresis and gel mobility shift experiments, we concluded that DREF is associated with the 86-kDa polypeptide. On gel filtration chromatography, a single peak of DREF activity was recovered in fractions corresponding to a molecular mass of 170 kDa, and the 86-kDa polypeptide was detected only in the corresponding fractions; thus, active DREF is probably a homodimeric form of the 86-kDa polypeptide. DREF may play important roles in coordinating expressions of Drosophila DNA replication-related genes.
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PMID:Novel 8-base pair sequence (Drosophila DNA replication-related element) and specific binding factor involved in the expression of Drosophila genes for DNA polymerase alpha and proliferating cell nuclear antigen. 809 16

The mosquito homolog of mammalian DNA polymerase epsilon, formerly known as a proliferating cell nuclear antigen (PCNA)-independent form of DNA polymerase delta, has been purified from mosquito larval extracts. The polymerase epsilon was separated from DNA polymerase alpha by chromatography on hydroxylapatite, and the enzyme was subsequently purified on single-stranded DNA agarose, followed by a 5' AMP-agarose chromatography step. The purified polymerase exhibits an intrinsic 3'-5' exonuclease activity and shows high activity using an oligo-primed DNA template. Neither human nor Drosophila PCNA stimulated this polymerase activity. Additional immunochemical and biochemical evidence indicates that this enzyme is distinct from DNA polymerase alpha.
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PMID:Mosquito DNA polymerase epsilon. 809 89

Exposure of normal adult human skin to doses of UV irradiation that induced mild sunburn resulted in the rapid appearance of p53 protein in the epidermis and superficial dermal fibroblasts. Immunohistological analysis with a panel of antibodies established that while p53 staining was not seen in normal skin it appeared within 2 h of UV exposure. The level of p53 immunostaining peaked at 24 h and returned to undetectable levels within 360 h. The induction of proliferating cell nuclear antigen (PCNA) (which is required for both DNA replication and repair) followed a similar spatial and temporal pattern to p53. The UV irradiation did not induce a mitotic response or the replication-associated antigens DNA polymerase alpha or Ki67. The accumulation of high levels of p53 and PCNA in response to UV doses to which many human populations are routinely exposed provides strong support for a model in which normal p53 acts as part of the DNA damage response in vertebrate cells. Such a model is consistent with the profound tumour-suppressor function of the p53 gene, the high rate of p53 mutation in neoplasia and the exceptionally high tumour susceptibility of p53-deficient mice.
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PMID:High levels of p53 protein in UV-irradiated normal human skin. 809 10

The recurrence rate of pituitary adenomas has been reported to be as high as 10% to 35% despite their generally benign nature. A monoclonal antibody directed against proliferating cell nuclear antigen (PCNA) was used to investigate whether the proliferative index might help to predict adenoma recurrence. This antigen is a nuclear protein identified as the auxiliary protein of deoxyribonucleic acid polymerase delta, and its gene expression correlates with cell proliferation. The authors studied 30 patients with recurrent pituitary adenomas, 32 with nonrecurrent adenomas, and seven normal pituitary tissue samples. The mean interval to recurrence ( +/- standard error of the mean) was 5.3 +/- 0.7 years. The age- and sex-matched nonrecurrent group had a mean follow-up period of 6.6 +/- 0.3 years without clinical recurrence. Mean percentages of PCNA-positive tumor nuclei in both the initial and the second surgical specimens of the recurrent adenomas (13.45% +/- 3.02% and 19.56% +/- 3.66%, respectively) were significantly higher than that of the nonrecurrent group (2.49% +/- 1.21%). In addition, recurrent tumors had a higher PCNA index than the initial tumors in the same patients. Normal anterior pituitary gland tissue had a significantly lower mean PCNA index (0.12% +/- 0.11%) than either patient group. Stepwise multivariate regression analysis indicated that factors which collectively correlated significantly with recurrence were: high PCNA index, large tumor size, extrasellar extension, and incomplete surgical excision. The PCNA nuclear count was not associated with age, sex, or hormone hypersecretion, but was higher in macro- than in microadenomas, in tumors with extrasellar extension, and in those incompletely excised. A higher PCNA index also correlated with a shorter disease-free interval. The authors conclude that evaluation of the PCNA index assists in predicting the likelihood of pituitary adenoma recurrence.
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PMID:Significance of proliferating cell nuclear antigen index in predicting pituitary adenoma recurrence. 809 73

Immunohistochemical detection of the nuclear antigen recognised by the monoclonal antibody Ki67, DNA polymerase alpha, and the proliferating cell nuclear antigen (PCNA), and histochemical staining for the argyrophilic proteins associated with the nucleolar organizer regions (AgNOR) were carried out on histological sections from 107 colorectal adenomas containing invasive carcinoma (ACIC), including 7 with regional lymph node metastases. Separate evaluations were made for fields corresponding to adenoma with low-grade dysplasia, adenoma with high-grade dysplasia and early cancer. The same techniques were also employed in 20 cases of normal mucosa and 20 advanced carcinomas. The mean percentages of Ki67, DNA polymerase alpha, and PCNA-positive nuclei and the number of AgNOR per nucleus progressively increased along the sequence from normal mucosa via low-grade and high-grade dysplasia adenoma to advanced cancer, whereas the early cancer values were not significantly different from those in the low-grade dysplasia areas. No significant difference in PCNA positivity and number of AgNOR were noted in ACIC with and without lymph node metastases. It is suggested that the decrease in proliferative activity thus revealed in early cancer may be due to changes in the submucosa microenvironment caused by invasion, and that the metastatic potential of an early colorectal cancer cannot be correlated to such activity.
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PMID:Cell proliferation in colorectal adenomas containing invasive carcinoma. 809 91


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