Size distribution and maturation of newly replicated DNA through the S and G2 phases of physarum polycephalum

Funderud, Steinar; Andreassen, Rolf; Haugli, Finn

doi:10.1016/0092-8674(78)90074-0

Cited by 57 publications

(25 citation statements)

References 20 publications

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“…Plotting the nascent strand lengths against time in S phase (Figure 4C) revealed an average rate of 0.9 kb/min/replicon for proP replicon. Although the rate of elongation of proP replicon has been evaluated to be more than twice greater than the one of php replicon, this value is in agreement with the canonical mean of 1.2 kb/min/replicon that has been calculated for Physarum (35). We thus conclude that php replicon is characterized by an unusually slow progression of replication forks.…”

Section: Resultssupporting

confidence: 83%

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Low rate of replication fork progression lengthens the replication timing of a locus containing an early firing origin

Bénard¹,

Maric²,

Pierron³

2007

Nucleic Acids Research

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Invariance of temporal order of genome replication in eukaryotic cells and its correlation with gene activity has been well-documented. However, recent data suggest a relax control of replication timing. To evaluate replication schedule accuracy, we detailed the replicational organization of the developmentally regulated php locus that we previously found to be lately replicated, even though php gene is highly transcribed in naturally synchronous plasmodia of Physarum. Unexpectedly, bi-dimensional agarose gel electrophoreses of DNA samples prepared at specific time points of S phase showed that replication of the locus actually begins at the onset of S phase but it proceeds through the first half of S phase, so that complete replication of php-containing DNA fragments occurs in late S phase. Origin mapping located replication initiation upstream php coding region. This proximity and rapid fork progression through the coding region result in an early replication of php gene. We demonstrated that afterwards an unusually low fork rate and unidirectional fork pausing prolong complete replication of php locus, and we excluded random replication timing. Importantly, we evidenced that the origin linked to php gene in plasmodium is not fired in amoebae when php expression dramatically reduced, further illustrating replication-transcription coupling in Physarum.

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Section: Resultssupporting

confidence: 83%

“…The curves allowed the measurement of fork rate at each locus during this period of S phase. The mean rate curve corresponds to the mean rate of replicons in plasmodia as measured by (35). ( D ) Table comparing data on php replicon elongation obtained by 2D-gel and alkaline gel experiments.…”

Section: Resultsmentioning

confidence: 99%

Low rate of replication fork progression lengthens the replication timing of a locus containing an early firing origin

Bénard¹,

Maric²,

Pierron³

2007

Nucleic Acids Research

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“…Since the rate observed fo r merging of replicons is slower than expected fr om the rate of replication fo rk movement (5-7, 231), completion of rep Ii cons represents a rate-limiting step in chromosome replication (5,7,231). This suggests that replication of a given chromoso mal region is completed only when all replicons in that cluster are ready to merge.…”

Section: Completion Of Repliconsmentioning

confidence: 93%

Replication of Eukaryotic Chromosomes: A Close-up of the Replication Fork

DePamphilis¹,

Wassarman²

1980

Annu. Rev. Biochem.

317

106

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“…We chose strain Tu 291 for several reasons: (i) it is the best-characterized strain of Physarum with respect to the mechanisms of DNA replication (28,29); (it) its precise synchrony of replication throughout S phase has recently been proven and the kinetics of DNA synthesis has been accurately established by high-resolution flow cytometry (30); (iii) it is known to be fully sensitive to the thymidylate synthesis inhibitor 5'-fluorodeoxyuridine (31), which is advantageous for maximal BrdUrd incorporation into DNA. Since strain Tu 291 is a derivative of the strain Wis 1 (19), we reasoned that the HindIII fragments containing actin-like sequences should be identifiable from the hybridization pattern of the parent strain (17).…”

Section: Resultsmentioning

confidence: 99%

Invariant temporal order of replication of the four actin gene loci during the naturally synchronous mitotic cycles of Physarum polycephalum.

Pierron¹,

Durica²,

Sauer³

1984

Proc. Natl. Acad. Sci. U.S.A.

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The chronological sequence of replication for the four unlinked actin gene loci of Physarum has been established. Southern hybridization analysis of density-labeled, bromodeoxyuridine-substituted DNA isolated from defined periods of S phase demonstrates that three actin loci (ard, ardC, ardO) are duplicated laVy, corresponding to the first 10% of the genome. The fourth locus (ard4) replicates later, between 80 and 100 min into S phase and after 75% of DNA synthesis is completed. Gene-dosage determinations, based on the quantitation of hybridization signals from DNAs isolated from various tinmes during S phase, confirm the results obtained with bromodeoxyuridine-substituted DNA and increase the temporal resolution. The chronological order of replication in the macroplasmodium appears constant through two consecutive cell cycles and after prolonged growth in suspension culture. The precise chronology of DNA synthesis at the gene level extends to the coordinate replication of allele pairs.It has been clearly demonstrated, both by cytological methods and density-labeling, that certain segments -of the eukaryotic genome replicate at defined time intervals in S phase of the cell cycle (1, 2) in lower eukaryotes like Physarum (3) as well as in human cells (4). Heterochromatin is generally, found to replicate late in S phase (5-7), whereas certain potentially active genes (8, 9) replicate early. Employing electron microscopic spreads of chromatin, we have recently visualized actively transcribing genes in early-replicated DNA of Physarum. Typically, both coding strands of a newly replicated locus are transcribed in early S phase (10). A relationship between the onset of DNA replication in S phase and transcription has been documented for yeast (11), Drosophila qmbryos (17), and tissue culture cells (13,14) (16,18), the evidence for the temporal order of DNA synthesis (3), and tfhe preferential transcription of newly replicated DNA in early S phase (10, 15), prompted us to determine the chronology of replication of the four actin loci.In this communication we demonstrate that three of the four actin loci are replicated at the time when only 5-10% of the genome has replicated. The synchrony of DNA replication at the gene level is such that two allelic DNA sequences of one actin locus are coordinately replicated. The fourth actin locus is replicated when DNA synthesis is 75% completed. Moreover, this temporal order of replication remains invariant, when monitored either through two consecutive S phases in a single macroplasmodium or over a period of at least 400 generation times in suspension culture. The significance of this fixed order of replication is discussed in light of the replication-transcription-coupling hypothesis. MATERIALS AND METHODSCultures. The strain Tu 291, provided by F. Haugli (Tromso University, Norway), was used throughput this investigation. Obtained by crossing stains RSD4 by'RSD8 amoebae, it is 'a diploid derivative of the Wis 1 natural isolate (19). The synchronous cultures (macroplasm...

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Size distribution and maturation of newly replicated DNA through the S and G2 phases of physarum polycephalum

Cited by 57 publications

References 20 publications

Low rate of replication fork progression lengthens the replication timing of a locus containing an early firing origin

Low rate of replication fork progression lengthens the replication timing of a locus containing an early firing origin

Replication of Eukaryotic Chromosomes: A Close-up of the Replication Fork

Invariant temporal order of replication of the four actin gene loci during the naturally synchronous mitotic cycles of Physarum polycephalum.

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