Actinomycin inhibits
DNA transcription.
The Phenoxazone ring is a flat structure and sticks between the two chains of the
DNA helix at
GC base pairs (called intercalation) and the cyclic
peptides (the other names in the figure) bind to the narrow groove of the helix. Because it is squeezed into the helix, it isn't possible to transcribe the
DNA into
mRNA.
At low concentrations, actinomycin D appears to inhibit transcription in
prokaryotes as wel as
eukaryotes, without affecting DNA
replication or
protein synthesis itself. The specific activity of it is not only used as an antibiotic, but also during treatment of some cancers (becaue of this inhibition of growth of rapid dividing cells).
Actinomycin originates from the
Streptomyces family.
Structure of Actinomycin D
O O
|| ||
------- C C-----------------
| | | |
| L-Methylvaline L-Methylvaline |
| | | |
| O=C C=O |
| | | |
| Sacrosine Sacrosine |
| | | |
| O=C C=O |
| | | |
| L-Proline L-Proline |
| | | |
| O=C C=O |
| | | |
| D-Valine D-Valine |
| | | |
| O=C C=O |
| | | |
|---L-Treonine L-Treonine--------|
| |
C=O O=C
| |
Phenoxazone ring