Abstract
Crithidia fasciculata kinetoplast DNA is a mitochondrial DNA composed of 5000 minicircles and ~ 25 maxicircles, all catenated into a giant network. By comparing the linking number of minicircles released from the network by limited sonication with that of control minicircles, we demonstrate that not only does the elaborate catenation of the network not cause supercoiling, but that there is no minicircle supercoiling at all. The absence of catenation-induced supercoiling is explained by our finding [using electron microscopy (EM) and gel electrophoresis] that network minicircles are joined by only one interlock; single interlocking can be accommodated without helix distortion. EM revealed that propidium diiodide supertwists all the network minicircles and thereby condenses the network into a much smaller size while maintaining its planarity. At high dye concentration the network is condensed to a size comparable to that found in vivo. Nevertheless, network minicircles bind less propidium than free minicircles, indicating that catenation into a network restricts the supercoiling of individual rings. These studies show that the mitochondrion of trypanosomatids may be a unique niche in nature where a covalently-closed circular DNA is not supercoiled. This absence of supercoiling may be a major factor in promoting the formation of the network.
Original language | English (US) |
---|---|
Pages (from-to) | 403-411 |
Number of pages | 9 |
Journal | EMBO Journal |
Volume | 12 |
Issue number | 2 |
DOIs | |
State | Published - 1993 |
Externally published | Yes |
Keywords
- Crithidia fasciculata
- Kinetoplast
- Minicircle
- Mitochondria
- Supercoiling
ASJC Scopus subject areas
- General Neuroscience
- Molecular Biology
- General Biochemistry, Genetics and Molecular Biology
- General Immunology and Microbiology