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The induction of chromosome aberrations by restriction endonucleases that produce blunt-end or cohesive-end
1University of Tennessee-Oak Ridge Graduate School of Biomedical Sciences 37831.
Abstract:
Restriction endonucleases have been used to study the involvement of specific types of DNA damages in the production of chromosome aberrations. In this study restriction endonucleases were introduced into viable CHO cells using osmolytic shock of pinocytic vesicles. We compared two cohesive-end cutters, Msp I (CCGG-2-base overlap) and Sau3A I (GATC-4-base overlap) with two blunt-end cutters, Alu I (AGCT) and Rsa I (GTAC). All 4 enzymes were effective at inducing aberrations. The 4-base overlap cohesive-end cutter Sau3A I was approximately as effective as the blunt-end cutter Alu I. We present evidence that cutting frequency rather than cut end-structure is important in determining efficiency of aberration induction. There is over-dispersion of the distribution of dicentrics and rings among cells, and the data could be fitted to a Neyman Type A distribution, a modified Poisson, that indicates that there is a probability distribution both for the entry of the enzyme into a cell nucleus and for the induction of aberrations once the enzyme has entered a cell nucleus. In addition, we used Alu I to determine the sensitivity of cells to aberration induction in the different stages of the cell cycle. Alu I induced aberrations in all stages of the cycle, chromatid-type in S/G2 and chromosome-type in G1. In agreement with data of others, there were variations in sensitivity with cycle stage, and changes in the proportions of the different aberration classes for chromatid-type aberrations.
Insights
Restriction endonucleases induced chromosome aberrations in cells. Cutting frequency, not DNA cut-end structure, determined aberration induction efficiency, with variations across the cell cycle.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Restriction endonucleases are tools for studying DNA damage and chromosome aberrations.
- Understanding how DNA damage affects chromosome stability is crucial in genetics.
Purpose of the Study:
- To investigate the role of different restriction endonuclease properties in inducing chromosome aberrations.
- To compare the efficiency of cohesive-end and blunt-end DNA cutters in aberration induction.
- To analyze the cell cycle-dependent sensitivity to DNA damage-induced aberrations.
Main Methods:
- Chinese Hamster Ovary (CHO) cells were treated with restriction endonucleases (Msp I, Sau3A I, Alu I, Rsa I) via osmolytic shock.
- Enzyme effectiveness was assessed by observing chromosome aberration induction.
- Cell cycle sensitivity was determined using Alu I across different cell cycle stages.
Main Results:
- All four tested restriction endonucleases effectively induced chromosome aberrations.
- Cutting frequency, rather than the type of DNA cut (cohesive-end vs. blunt-end), was key to aberration induction efficiency.
- Aberration distribution followed a Neyman Type A distribution, suggesting probabilistic enzyme entry and aberration induction.
- Alu I induced aberrations in all cell cycle stages, with chromatid-type aberrations in S/G2 and chromosome-type in G1.
Conclusions:
- Restriction endonuclease cutting frequency is a primary determinant of chromosome aberration induction.
- Enzyme entry into the nucleus and subsequent aberration induction are probabilistic events.
- Cell cycle stage influences sensitivity to DNA damage and the types of aberrations induced.