Visualization of Drosophila melanogaster chorion genes undergoing amplification
The authors visualized by electron microscopy the preferential amplification of Drosophila chorion genes in late-stage follicle cells. Chromatin spreads revealed large clusters of actively transcribed genes of the appropriate size, spacing, and orientation for chorion genes that were expressed with the correct temporal specificity. Occasionally the active genes were observed within or contiguous with intact replicons and replication forks. In every case, our micrographs are consistent with the hypothesis that the central region of each chorion domain contains a replication origin(s) used during the amplification event. In one case, a small replication bubble was observed precisely at the site of the essential region of the X chromosome amplification control element. The micrographs also suggest that forks at either end of a replicon frequently progress very different distances, presumably due to different times in initiation or different rates of movement. It appears that all chorion genes (even those coding for minor proteins) are transcribed in a ''fully on'' condition, albeit for varied durations, and that if replication fork passage does inactivate a promoter, it does so very transiently. Furthermore, a DNA segment containing one active gene is likely to have an additional active gene(s). Surprisingly, during the time frame of expected maximum activity, approximately half of the chorion sequences appear transciptionally inactive.
- Research Organization:
- Dept. of Microbiology Cancer Center, Molecular Biology Institute, Univ. of Virginia, Charlottesville, VA (US)
- OSTI ID:
- 6469723
- Journal Information:
- Mol. Cell. Biol.; (United States), Vol. 8:7
- Country of Publication:
- United States
- Language:
- English
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CELL DIFFERENTIATION
MOLECULAR BIOLOGY
DROSOPHILA
GENETIC MAPPING
FETAL MEMBRANES
ONTOGENESIS
REPLICONS
BIOLOGICAL FUNCTIONS
X CHROMOSOME
GENE AMPLIFICATION
CHROMATIN
DNA REPLICATION
ELECTRON MICROSCOPY
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CHROMOSOMES
DIPTERA
FLIES
FRUIT FLIES
FUNCTIONS
GENES
HETEROCHROMOSOMES
INSECTS
INVERTEBRATES
MAPPING
MEMBRANES
MICROSCOPY
NUCLEIC ACID REPLICATION
550400* - Genetics
550200 - Biochemistry
550800 - Morphology