Actionmycin-D -This antibiotic is more used as a research tool, rather than for clinical purposes, because of its high toxicity. It suppresses DNA dependent RNA synthesis at much lower concentrations than it inhibits DNA replication. Structurally it consists of cyclic pentapeptide lactones. It acts on dsDNA containing guanine, with which it interacts, and is believed to insert into the minor groove of DNA to form up to seven bonds with adjacent parts of the molecule. Guanine provides an H atom lying in the minor groove for binding with the quinoid oxygen of actinomycin D. According to an alternative model, actinomycin D may intercalate with the DNA.
