Chromosomal Replicons of Higher Plants

Hof, J. Van’t

doi:10.1007/978-1-4613-1037-2_3

Cited by 5 publications

(4 citation statements)

References 58 publications

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“…This is in agreement with the expectation that a single Ac will exist in a state of partial replication only briefly during the chromosome replication cycle. Given a rate of replication of DNA in plants of 0.4 kb/min, we can calculate that it will take about 12 min for the 4.6-kb Ac element to complete replication, a small fraction of the several hours that it takes an actively dividing plant cell to complete the replication process (31)(32)(33). We hypothesize that the distance separating the directly repeated elements of a chromosome-breaking macrotransposon must be short enough so that the ends of the nonadjacent elements serve frequently as cosubstrates for transposition, but long enough so that the time of replication of the entire macrotransposon is a significant proportion of the replicon's doubling time.…”

Section: Resultsmentioning

confidence: 99%

“…We hypothesize that the distance separating the directly repeated elements of a chromosome-breaking macrotransposon must be short enough so that the ends of the nonadjacent elements serve frequently as cosubstrates for transposition, but long enough so that the time of replication of the entire macrotransposon is a significant proportion of the replicon's doubling time. In the fAc Ac macrotransposon, the distance between the ends of the border elements is >25 kb, which is at least half of the size of the average monocot replicon (33).…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Chromosome-breaking structure in maize involving a fractured Ac element.

Ralston¹,

English²,

Dooner³

1989

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

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Chromosome breakage in maize can result from an interaction between certain transposable elements. When an Ac (Activator) element and a state I Ds (Dissociation) element are present together in the genome, either linked or unlinked, breaks occur regularly at the locus of the Ds element. We show here that breaks occur with high frequency at or near the locus of a structure consisting of a 2.5-kilobase (kb) terminally deleted or fractured Ac element very tightly linked to a second, intact 4.6-kb Ac element. This structure has the features of a macrotransposon and may behave like one. Loss of the tight linkage abolishes chromosome breakage. A model based on transposition of the macrotransposon is proposed to explain the chromosome-breaking properties of Ac and Ds.Chromosome breakage was the first manifestation of transposable element activity detected by McClintock. She formulated the concept of transposition based on her observations that the position of breaks in the short arm of chromosome 9 (chromosome 9S) could change in some of her stocks. In 1946, she reported the existence of a locus proximal to wx (waxy endosperm) at which breaks tended to occur (1). She called the locus Ds (Dissociation) and established that breaks would occur at the locus only when a second factor, which she termed Ac (Activator), was present in the genome (2). Subsequently, she demonstrated that Ds did not occupy a fixed locus but could transpose to locations in chromosome 9S distal to wx and other genes specifying endosperm traits [colorless kernel (c), shrunken endosperm (sh), and bronze (bz)]. The altered position of chromatid breaks was readily recognized by the changes in kernel phenotypes that were produced when breaks initiated at different positions in chromosome 9S and was confirmed by cytological and genetic tests (3).The ability to break chromosomes is not, however, a general feature of Ds transposable elements. McClintock distinguished between state I Ds elements that produced many detectable breaks and few reversions when inserted in a known gene and state II Ds elements that produced higher rates of reversion and lower-to-undetectable rates of chromosome breaks (4). These states differ in relative stability: whereas state II is very stable, state I is unstable and changes frequently to state II.Two insertions in different sh mutants borne on chromosomes harboring state I Ds elements in the vicinity of the sh locus (5) have been characterized molecularly. The unstable sh mutants sh-m:5933 and sh-m:6233 carry unusual insertions that, though of dissimilar sizes [>30 kilobases (kb) vs. 4 kb], share a structure that has been termed "double Ds" (6, 7). This structure consists of two identical copies of a 2-kb internal deletion derivative of the 4.6-kb autonomous Ac element, arranged so that one copy is inserted, in reverse orientation, into the second copy. Double Ds has been postulated to be involved in chromosome breakage based on the correlation between its presence in the above mutants and the occurrence of chromosom...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Chromosome-breaking structure in maize involving a fractured Ac element.

Ralston¹,

English²,

Dooner³

1989

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

View full text Add to dashboard Cite

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“…at the University of Twente [40, 411. The method involves the use of two successive quench steps: the first initiates the formation of an interfacial, dense skin layer; the second initiates phase separation in the bulk membrane structure. The thickness of the selective skin layer is determined primarily by the contact time of the membrane with the first quench medium [40]. The process steps are shown schematically in Fig.…”

Section: Zntegrally Skinned Asymmetric Membranes and Multicomponent Amentioning

confidence: 99%

Recent advances in the formation of ultrathin polymeric membranes for gas separations

Pinnau

1994

Polymers for Advanced Techs

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During the past 20 years membrane systems have been applied to a limited number of commercial gas separations. To further advance membrane‐based gas separations, current research efforts focus on optimization of (i) membrane materials, (ii) membrane structures and (iii) membrane system design. In this overview, recent developments in the formation of high‐performance gas separation membranes are discussed. The gas separation properties of state‐of‐the‐art integrally skinned asymmetric membranes and thin‐film composite membranes are summarized. Future directions for the preparation of advanced gas separation membranes are highlighted.

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“…In the meristem roots of vascular plants, it was shown that IOD and FR are not correlated with S length, and the S length is instead regulated through replicon family staggering [119], where the late origins are fired after a 'tempo-pause' [130]. The presence of a correlation between vascular plant S phase duration and genome size (see above) is due to relatively strict limits on the number of replicons simultaneously active in a plant nucleus.…”

Section: Examples Of S Phase Duration Regulationmentioning

confidence: 99%

S Phase Duration Is Determined by Local Rate and Global Organization of Replication

Greenberg

Simon

2022

Biology

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The duration of the cell cycle has been extensively studied and a wide degree of variability exists between cells, tissues and organisms. However, the duration of S phase has often been neglected, due to the false assumption that S phase duration is relatively constant. In this paper, we describe the methodologies to measure S phase duration, summarize the existing knowledge about its variability and discuss the key factors that control it. The local rate of replication (LRR), which is a combination of fork rate (FR) and inter-origin distance (IOD), has a limited influence on S phase duration, partially due to the compensation between FR and IOD. On the other hand, the organization of the replication program, specifically the amount of replication domains that fire simultaneously and the degree of overlap between the firing of distinct replication timing domains, is the main determinant of S phase duration. We use these principles to explain the variation in S phase length in different tissues and conditions.

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Chromosomal Replicons of Higher Plants

Cited by 5 publications

References 58 publications

Chromosome-breaking structure in maize involving a fractured Ac element.

Chromosome-breaking structure in maize involving a fractured Ac element.

Recent advances in the formation of ultrathin polymeric membranes for gas separations

S Phase Duration Is Determined by Local Rate and Global Organization of Replication

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