actinomycin

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(ăk'tə-nō-mī'sĭn)
n.

Any of a large group of red, often toxic, polypeptide antibiotics isolated from soil bacteria of several species of Streptomyces (originally Actinomyces) that are active against gram-positive bacteria and fungi.

any of a large group of antibiotics isolated from various species of Streptomyces bacteria and characterized by having a substituted phenoxazine ring linked to two cyclic heterodetic peptides. The principal member of the group is actinomycin D (also called actinomycin C₁, actinomycin IV), which, at low concentrations, inhibits transcription without appreciably affecting DNA replication in both prokaryotic and eukaryotic cells. Actinomycin D binds tightly to duplex DNA thereby preventing it from being an effective template for RNA synthesis. Spectroscopic and hydrodynamic studies of complexes of actinomycin D and DNA suggest that the phenoxazine ring of actinomycin is intercalated between neighbouring base pairs in DNA. Other conformational studies indicate that actinomycin D recognizes the base sequence GpC in DNA.

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A family of antibiotics from various species of Streptomyces, which are active against bacteria and fungi; it includes the antineoplastic agents actinomycin C (cactinomycin) and actinomycin D (dactinomycin).