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At least 325 records · Page 18Linked to original sources
PubMed1978

The structure and maturation of intermediates in bacteriophage T7 DNA replication.

Concatemeric DNA from T7-infected cells consists of phage genomes in a linear head-to-tail arrangement. Adjacent genomes within a concatemer overlap for the length of the terminal repetition. Fast-sedimenting T7 DNA contains single-stranded regions at roughly unit-lentth intervals but these interruptions are heterogeneously distributed and do not occur at the genetic termini. Mutations in either bacteriophage genes 9, 18, or 19 (required for DNA maturation and packaging) lead to the synthesis and persistence of DNA with fewer interruptions than normal.

Base Sequence↗
PubMed1982

Purification of the cdc8 protein of Saccharomyces cerevisiae by complementation in an aphidicolin-sensitive in vitro DNA replication system.

DNA synthesis in vitro in Brij-treated Saccharomyces cerevisiae requires the product of the CDC8 gene (Hereford, L. M. & Hartwell, L. H. (1971) Nature (London) New Biol. 234, 171-172). Extracts of wild-type A364a yeast restore DNA synthesis in Brij-treated cdc8, a mutant containing a thermolabile cdc8 gene product. This constitutes a complementation assay by which the cdc8 gene product can be monitored during purification. A heat-stable protein responsible for this complementation has been partially purified from both wild-type A364a cells and from a cdc8 temperature-sensitive mutant. The complementation activity from the mutant is thermolabile when compared to the wild-type activity, indicating that CDC8 is the structural gene for the protein.

Aphidicolin↗
PubMed2002

Ku antigen, an origin-specific binding protein that associates with replication proteins, is required for mammalian DNA replication.

Ors binding activity (OBA) represents a HeLa cell protein activity that binds in a sequence-specific manner to A3/4, a 36-bp mammalian replication origin sequence. OBA's DNA binding domain is identical to the 80-kDa subunit of Ku antigen. Ku antigen associates with mammalian origins of DNA replication in vivo, with maximum binding at the G1/S phase. Addition of an A3/4 double-stranded oligonucleotide inhibited in vitro DNA replication of p186, pors12, and pX24, plasmids containing the monkey replication origins of ors8, ors12, and the Chinese hamster DHFR oribeta, respectively. In contrast, in vitro SV40 DNA replication remained unaffected. The inhibitory effect of A3/4 oligonucleotide was fully reversed upon addition of affinity-purified Ku. Furthermore, depletion of Ku by inclusion of an antibody recognizing the Ku heterodimer, Ku70/Ku80, decreased mammalian replication to basal levels. By co-immunoprecipitation analyses, Ku was found to interact with DNA polymerases alpha, delta and epsilon, PCNA, topoisomerase II, RF-C, RP-A, DNA-PKcs, ORC-2, and Oct-1. These interactions were not inhibited by the presence of ethidium bromide in the immunoprecipitation reaction, suggesting DNA-independent protein associations. The data suggest an involvement of Ku in mammalian DNA replication as an origin-specific-binding protein with DNA helicase activity. Ku acts at the initiation step of replication and requires an A3/4-homologous sequence for origin binding. The physical association of Ku with replication proteins reveals a possible mechanism by which Ku is recruited to mammalian origins.

Animals↗
PubMed2001

Multiple phosphorylation sites of DNA polymerase alpha-primase cooperate to regulate the initiation of DNA replication in vitro.

DNA polymerase alpha-primase (pol-prim) is the only enzyme that can start DNA replication de novo. The 180-kDa (p180) and 68-kDa (p68) subunits of the human four-subunit enzyme are phosphorylated by Cyclin-dependent kinases (Cdks) in a cell cycle-dependent manner. Cyclin A-Cdk2 physically interacts with pol-prim and phosphorylates N-terminal amino acids of the p180 and the p68 subunits, leading to an inhibition of pol-prim in initiating cell-free SV40 DNA replication. Mutation of conserved putative Cdk phosphorylation sites in the N terminus of human p180 and p68 reduced their phosphorylation by Cyclin A-Cdk2 in vitro. In contrast to wild-type pol-prim these mutants were no longer inhibited by Cyclin A-Cdk2 in the initiation of viral DNA replication. Importantly, rather than inhibiting it, Cyclin A-Cdk2 stimulated the initiation activity of pol-prim containing a triple N-terminal alanine mutant of the p180 subunit. Together these results suggest that Cyclin A-Cdk2 executes both stimulatory and inhibitory effects on the activity of pol-prim in initiating DNA replication.

Animals↗
PubMed1994

DNA replication arrest and tolerance to DNA methylation damage.

Inhibition of DNA replication by different DNA damaging agents has been investigated in HeLaMR cells and a methylation damage-tolerant variant HeLa5A1. In synchronous HeLaMR and HeLa5A1 cells exposed to N-ethyl-N-nitrosourea or ionizing radiation in mid-G1 phase, DNA synthesis was inhibited in the following S phase. N-methyl-N-nitrosourea-induced replication inhibition in HeLaMR cells was delayed until the second S phase after treatment. In contrast, N-methyl-N-nitrosourea treatment of HeLa5A1 cells affected neither the timing nor the extent of the first or second S phases. Both radiation and chemical treatment inhibited replication of an episomal plasmid and of genomic DNA in unison. Inhibition was observed at levels of DNA damage that did not directly damage the plasmid molecules. Thus, DNA replication inhibition occurs immediately after ionizing radiation or ethylation damage, but methylation damage requires processing through one cell cycle to generate an inhibitory signal. The inhibitory signal appears to act in trans on undamaged DNA. Although methylation-tolerant cells are responsive to inhibition after gamma-irradiation, methylation damage does not produce inhibitory signals to which they respond.

DNA Damage↗
PubMed2001

The temperature sensitive mutant p53-143ala extends in vitro life span, promotes errors in DNA replication and impairs DNA repair in normal human oral keratinocytes.

Many human cancers contain a hemizygous point missense mutation in p53, allowing expression of both wild-type and mutant p53. To understand the relationship between wild-type and mutant p53 in cells, we investigated the influence of a naturally occurring temperature-sensitive mutant p53 (valine to alanine substitution at codon 143: mp53-143ala) on the life span of normal human oral keratinocytes (NHOK) and the expression of wild-type p53. We also investigated the effect of the mutant p53 on the genetic stability of NHOK. The mp53-143ala extended the in vitro life span of NHOK by four-fold, but failed to overcome the M2 crisis stage for immortalization. The mp53-143ala notably suppressed wild-type p53 in NHOK at post-transcriptional levels. Moreover, the mp53-143ala notably increased both spontaneous and genotoxic agent-induced mutation frequency of a shuttle vector in NHOK. These data indicate that mutant p53 induces genetic instability by, in part, inhibiting the expression of wild-type p53 through a dominant negative role in cells expressing both mutant and wild-type p53.

Cell Death↗
PubMed2006

Chromatin loading of Smc5/6 is induced by DNA replication but not by DNA double-strand breaks.

Smc6, a member of the structural maintenance of chromosomes (SMC) family of proteins, forms a complex with related Smc5. Genetic analyses of yeast have demonstrated the involvement of Smc6 in DNA repair and checkpoint responses. In this study, we investigated the role of the Smc5/6 complex in higher eukaryotes by analyzing its behavior in Xenopus laevis egg extracts. Smc5/6 was loaded onto chromatin during DNA replication in a manner dependent on the initiation of DNA synthesis, and it dissociated from chromatin during mitosis. Moreover, the induction of DNA double-strand breaks following replication did not significantly affect the amount of chromatin-associated Smc6. These findings suggest that the Smc5/6 complex is regulated during the cell cycle, presumably in anticipation of DNA damage that may arise during replication.

Animals↗
PubMed1988

In situ enzymology of DNA replication and ultraviolet-induced DNA repair synthesis in permeable human cells.

Using permeable diploid human fibroblasts, we have studied the deoxyribonucleoside triphosphate concentration dependences of ultraviolet- (UV-) induced DNA repair synthesis and semiconservative DNA replication. In both cell types (AG1518 and IMR-90) examined, the apparent Km values for dCTP, dGTP, and dTTP for DNA replication were between 1.2 and 2.9 microM. For UV-induced DNA repair synthesis, the apparent Km values were substantially lower, ranging from 0.11 to 0.44 microM for AG1518 cells and from 0.06 to 0.24 microM for IMR-90 cells. Control experiments established that these values were not significantly influenced by nucleotide degradation during the permeable cell incubations or by the presence of residual endogenous nucleotides within the permeable cells. Recent data implicate DNA polymerase delta in UV-induced repair synthesis and suggest that DNA polymerases alpha and delta are both involved in semiconservative replication. We measured Km values for dGTP and dTTP for polymerases alpha and delta, for comparison with the values for replication and repair synthesis. Km values for polymerase alpha were 2.0 microM for dGTP and 5.0 microM for dTTP. For polymerase delta, the Km values were 2.0 microM for dGTP and 3.5 microM for dTTP. The deoxyribonucleotide Km values for DNA polymerase delta are much greater than the Km values for UV-induced repair synthesis, suggesting that when polymerase delta functions in DNA repair, its characteristics are altered substantially either by association with accessory proteins or by direct posttranslational modification. In contrast, the deoxyribonucleotide binding characteristics of the DNA replication machinery differ little from those of the isolated DNA polymerases.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Line↗
PubMedDate not supplied

Control of DNA replication: regulation and activation of eukaryotic replicative helicase, MCM.

DNA replication is a key event of cell proliferation and the final target of signal transduction induced by growth factor stimulation. It is also strictly regulated during the ongoing cell cycle so that it occurs only once during S phase and that all the genetic materials are faithfully duplicated. DNA replication may be arrested or temporally inhibited due to a varieties of internal and external causes. Cells have developed intricate mechanisms to cope with the arrested replication forks to minimize the adversary effect on the stable maintenance of genetic materials. Helicases play a central role in DNA replication. In eukaryotes, MCM (minichromosome maintenance) protein complex plays essential roles as a replicative helicase. MCM4-6-7 complex possesses intrinsic DNA helicase activity which translocates on single-stranded DNA form 3' to 5'. Mammalian MCM4-6-7 helicase and ATPase activities are specifically stimulated by the presence of thymine-rich single-stranded DNA sequences onto which it is loaded. The activation appears to depend on the thymine content of this single-strand, and sequences derived from human replication origins can serve as potent activators of the MCM helicase. MCM is a prime target of Cdc7 kinase, known to be essential for activation of replication origins. We will discuss how the MCM may be activated at the replication origins by template DNA, phosphorylation, and interaction with other replicative proteins, and will present a model of how activation of MCM helicase by specific sequences may contribute to selection of replication initiation sites in higher eukaryotes.

Animals↗
PubMed2005

Requirements for replication restart proteins during constitutive stable DNA replication in Escherichia coli K-12.

Constitutive stable DNA replication (cSDR) is a mechanism for replisome loading in Escherichia coli K-12. This occurs in a dnaA-independent fashion in an rnhA mutant. cSDR is dependent on recA, priA, and transcription. In this report, it is shown that dnaA rnhA mutants using cSDR for initiation of their DNA replication additionally require priB, but not priC, for viability. Two subtle priA missense mutations either eliminated the ability to grow using cSDR (priA301 C479Y) or resulted in very small colonies (priA300 K230R). DnaC809, a priA suppressor, failed to allow priA or priB mutants to grow using cSDR to initiate DNA replication. Furthermore, unlike dnaC(+) strains, dnaC809 strains require priC for cSDR. DnaC809,820, a priC-independent suppressor of priA2::kan phenotypes, allowed priA and priC (but not priB) mutants to grow using cSDR to initiate DNA replication. It is also shown that rep and rnhA mutations are synthetically lethal. DnaC809 and dnaC809,820 mutations suppress this lethality. Rep is further shown to be required for cSDR in a dnaC809 strain. A model whereby these different sets of replication restart proteins interact preferentially with substrates associated with either RecA or SSB during replication restart and cSDR, respectively, is proposed.

Bacterial Proteins↗
PubMed1978

[DNA replication in HeLa cells after gamma irradiation. II. The periodicity of DNA replication in the process of giant cell formation].

HeLa G-63 cells irradiated by 5 krads of 6 degrees Co gamma-rays 1.5--2 hours after mitosis (G1-phase) were incubated in growth medium during 9 days. The number of proliferating and eliminated cells, the content of DNA per cell nucleus, and kinetics of the labeled cell fraction upon 3H-TdR continuous incubation were studied. It has been concluded that: during the giant cell growth the nuclear DNA is replicated periodically without following mitoses; 90% of cells are involved in such a cycle; the duration of the period of DNA synthesis in giant cells is the same as that in non-irradiated cells; the duration of the gap between two successive S-periods in giant cells is 2--6 times as long as the sum of G2+M+G1 periods in the normal non-irradiated cells.

Cell Division↗
PubMed1996

The large subunit of replication factor C (Rfc1p/Cdc44p) is required for DNA replication and DNA repair in Saccharomyces cerevisiae.

We used genetic and biochemical techniques to characterize the phenotypes associated with mutations affecting the large subunit of replication factor C (Cdc44p or Rfc1p) in Saccharomyces cerevisiae. We demonstrate that Cdc44p is required for both DNA replication and DNA repair in vivo. Cold-sensitive cdc44 mutants experience a delay in traversing S phase at the restrictive temperature following alpha factor arrest; although mutant cells eventually accumulate with a G2/M DNA content, they undergo a cell cycle arrest and initiate neither mitosis nor a new round of DNA synthesis. cdc44 mutants also exhibit an elevated level of spontaneous mutation, and they are sensitive both to the DNA damaging agent methylmethane sulfonate and to exposure to UV radiation. After exposure to UV radiation, cdc44 mutants at the restrictive temperature contain higher levels of single-stranded DNA breaks than do wild-type cells. This observation is consistent with the hypothesis that Cdc44p is involved in repairing gaps in the DNA after the excision of damaged bases. Thus, Cdc44p plays an important role in both DNA replication and DNA repair in vivo.

Base Sequence↗
PubMed1999

Roles of LAP2 proteins in nuclear assembly and DNA replication: truncated LAP2beta proteins alter lamina assembly, envelope formation, nuclear size, and DNA replication efficiency in Xenopus laevis extracts.

Humans express three major splicing isoforms of LAP2, a lamin- and chromatin-binding nuclear protein. LAP2beta and gamma are integral membrane proteins, whereas alpha is intranuclear. When truncated recombinant human LAP2beta proteins were added to cell-free Xenopus laevis nuclear assembly reactions at high concentrations, a domain common to all LAP2 isoforms (residues 1-187) inhibited membrane binding to chromatin, whereas the chromatin- and lamin-binding region (residues 1-408) inhibited chromatin expansion. At lower concentrations of the common domain, membranes attached to chromatin with a unique scalloped morphology, but these nuclei neither accumulated lamins nor replicated. At lower concentrations of the chromatin- and lamin-binding region, nuclear envelopes and lamins assembled, but nuclei failed to enlarge and replicated on average 2. 5-fold better than controls. This enhancement was not due to rereplication, as shown by density substitution experiments, suggesting the hypothesis that LAP2beta is a downstream effector of lamina assembly in promoting replication competence. Overall, our findings suggest that LAP2 proteins mediate membrane-chromatin attachment and lamina assembly, and may promote replication by influencing chromatin structure.

Amino Acid Sequence↗
PubMed1986

Initiation of DNA replication in nuclei and purified DNA by a cell-free extract of Xenopus eggs.

We demonstrate that cell-free extracts prepared from activated eggs of X. laevis by a method similar to that of Lohka and Masui initiate and complete semiconservative DNA replication of sperm nuclei and plasmid DNA. The efficiency of replication is comparable to that in the intact egg. Under optimal conditions 70%-100% of nuclei, and up to 38% of naked DNA molecules replicate completely. Genuine initiation of replication occurs rather than elongation of preformed primers or priming of irreversibly denatured templates. Rereplication of templates is observed under certain conditions. In addition to replicating DNA, these extracts also assemble nucleus-like structures from naked DNA.

Animals↗