Related Experiment Videos
Monte-Carlo simulation of multisite echinomycin-DNA interactions detected by in vitro transcription analysis
D R Phillips1, R J White, D Dean
1Biochemistry Department, La Trobe University, Bundoora, Victoria, Australia.
Abstract:
The interaction of echinomycin with DNA was analyzed at 37 degrees C by in vitro transcription analysis using a 497 bp fragment of DNA containing the lac UV5 promoter. Sixteen discrete drug binding sites were detected. The mole fraction of blocked transcript at each site was monitored over 4 h, and the kinetic profile was analyzed by Monte-Carlo simulation. The time course for all 16 sites was fully described by this process. For each drug site, three parameters were resolved with the following variation between sites: relative drug occupancy (1-26), dissociation rate constant (0.06-0.70 min-1), and probability of termination of transcription (0-48%). Eight low-occupancy binding sites were at 5'-CA sequences (relative occupancy of 1.0-2.9). The eight major sites were all at 5'-CG sequences (relative occupancy of 6.3-26) and exhibited an average occupancy some 13-fold greater than the CA sites, corresponding to an average additional stability of approximately 1.6 kcal. The dissociation rates from apparent high-affinity sites were only partially correlated with relative occupancy. Ten binding sites exhibited a 3-48% probability of termination of transcription immediately adjacent to the 5'-CG central sequence. Termination probably arises from distortion of the DNA helix in regions flanking the binding site and was most dramatic (48% probability) where two adjacent CG sites were separated by only 1 bp. This termination phenomenon may well account for the observed effects of echinomycin in vivo.
Insights
Echinomycin binds to DNA at specific sites, with higher affinity for CG sequences. This binding influences transcription, potentially causing termination, which may explain its in vivo effects.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Echinomycin is a DNA-binding antibiotic.
- Understanding its precise interaction with DNA is crucial for its therapeutic applications and biological effects.
Purpose of the Study:
- To analyze the interaction of echinomycin with DNA at 37°C using in vitro transcription.
- To characterize the binding sites, occupancy, dissociation rates, and transcription termination probabilities.
Main Methods:
- In vitro transcription analysis using a DNA fragment with the lac UV5 promoter.
- Monitoring blocked transcript mole fraction over 4 hours.
- Kinetic profile analysis using Monte-Carlo simulation.
Main Results:
- Sixteen discrete drug binding sites were detected on the DNA fragment.
- Eight major binding sites were identified at 5'-CG sequences with high relative occupancy (6.3-26).
- Ten binding sites showed a 3-48% probability of transcription termination adjacent to 5'-CG sequences.
Conclusions:
- Echinomycin exhibits differential binding affinities for DNA sequences, favoring CG sites.
- DNA binding by echinomycin can lead to transcription termination, potentially explaining its in vivo activity.
- The study provides a detailed kinetic profile of echinomycin-DNA interactions.