noun

• Any of a group of substances with antibiotic and antineoplastic properties originally isolated from soil-dwelling microorganisms (actinomycetes) of the genus Streptomyces (formerly Actinomyces).

  Actinomycins were the first antibiotics to be isolated from soil bacteria. Their structure contains two peptide loops attached to a planar ring system, which binds to DNA and inhibits its transcription. The most important is actinomycin D, which is used in chemotherapy and biological research.