Abstract
The recovery of maize (Zea mays L.) chromosome addition lines of oat (Avena sativa L.) from oat x maize crosses enables us to analyze the structure and composition of individual maize chromosomes via the isolation and characterization of chromosome-specific cosmid clones. Restriction fragment fingerprinting, sequencing, and in situ hybridization were applied to discover a new family of knob associated tandem repeats, the TR1, which are capable of forming fold-back DNA segments, as well as a new family of centromeric tandem repeats, CentC. Analysis of knob and centromeric DNA segments revealed a complex organization in which blocks of tandemly arranged repeating units are interrupted by insertions of other repeated DNA sequences, mostly represented by individual full size copies of retrotransposable elements. There is an obvious preference for the integration/association of certain retrotransposable elements into knobs or centromere regions as well as for integration of retrotransposable elements into certain sites (hot spots) of the 180-bp repeat. DNA hybridization to a blot panel of eight individual maize chromosome addition lines revealed that CentC, TR1, and 180-bp tandem repeats are found in each of these maize chromosomes, but the copy number of each can vary significantly from about 100 to 25,000. In situ hybridization revealed variation among the maize chromosomes in the size of centromeric tandem repeats as well as in the size and composition of knob regions. It was found that knobs may be composed of either 180-bp or TR1, or both repeats, and in addition to large knobs these repeated elements may form micro clusters which are detectable only with the help of in situ hybridization. The association of the fold-back elements with knobs, knob polymorphism and complex structure suggest that maize knob may be consider as megatransposable elements. The discovery of the interspersion of retrotransposable elements among blocks of tandem repeats in maize and some other organisms suggests that this pattern may be basic to heterochromatin organization for eukaryotes.
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Claims 14
Claim · model-written summary
TR1 knob repeats can form fold-back DNA segments.
- Outcome
- TR1e0
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a new family of knob associated tandem repeats, the TR1, which are capable of forming fold-back DNA segments”
t0“maize”
Claim · model-written summary
CentC was identified as a centromeric tandem repeat family.
- Outcome
- CentCe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a new family of centromeric tandem repeats, CentC”
t0“maize”
Claim · model-written summary
Maize knob and centromeric repeat blocks are interrupted by other repeats.
- Outcome
- blocks of tandemly arranged repeating unitse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“blocks of tandemly arranged repeating units are interrupted by insertions of other repeated DNA sequences”
t0“maize”
Claim · model-written summary
Inserted sequences are mainly full-size retrotransposable elements.
- Outcome
- retrotransposable elementse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“mostly represented by individual full size copies of retrotransposable elements”
t0“maize”
Claim · model-written summary
Certain retrotransposable elements preferentially associate with knobs or centromeres.
- Outcome
- retrotransposable elementse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“obvious preference for the integration/association of certain retrotransposable elements into knobs or centromere regions”
t0“maize”
Claim · model-written summary
Retrotransposable elements preferentially integrate at hot spots of the 180-bp repeat.
- Outcome
- 180-bp repeate0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“integration of retrotransposable elements into certain sites (hot spots) of the 180-bp repeat”
t0“maize”
Claim · model-written summary
CentC, TR1 and 180-bp repeats occur on each tested maize chromosome.
- Outcome
- CentC, TR1, and 180-bp tandem repeatse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CentC, TR1, and 180-bp tandem repeats are found in each of these maize chromosomes”
t0“maize”
Claim · model-written summary
Repeat copy number varies significantly from about 100 to 25,000.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“copy number of each can vary significantly from about 100 to 25,000”
t0“maize”
Claim · model-written summary
Maize chromosomes vary in centromeric repeat size.
- Outcome
- size of centromeric tandem repeatse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“variation among the maize chromosomes in the size of centromeric tandem repeats”
t0“maize”
Claim · model-written summary
Maize chromosomes vary in knob size and composition.
- Outcome
- size and composition of knob regionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“size and composition of knob regions”
t0“maize”
Claim · model-written summary
Maize knobs contain 180-bp repeats, TR1 repeats, or both.
- Outcome
- knobse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“knobs may be composed of either 180-bp or TR1, or both repeats”
t0“maize”
Claim · model-written summary
Repeat elements also form micro clusters detectable only by in situ hybridization.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“repeated elements may form micro clusters which are detectable only with the help of in situ hybridization”
t0“maize”
Claim · model-written summary
Maize knobs may be considered megatransposable elements.
- Outcome
- maize knob may be consider as megatransposable elementse0
- Qualifier
- knob polymorphism and complex structuree0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“knob polymorphism and complex structure suggest that maize knob may be consider as megatransposable elements”
t0“maize”
Claim · model-written summary
Interspersed retrotransposable elements and tandem repeats may be a basic feature of eukaryotic heterochromatin organization.
- Outcome
- heterochromatin organization for eukaryotese0
- Qualifier
- interspersion of retrotransposable elements among blocks of tandem repeatse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“interspersion of retrotransposable elements among blocks of tandem repeats in maize and some other organisms suggests that this pattern may be basic to heterochromatin organization for eukaryotes”
t0“maize”