The actinomycins are a class of polypeptide antibiotics isolated from soil bacteria of the genus Streptomyces, of which the most significant's actinomycin D. It was the first antibiotic isolated by Selman Waksman and his co-worker H. B. Woodruff in 1940. Mechanism Actinomycin D's primarily used as an investigative tool in cell biology to inhibit transcription. It does this by binding DNA at the transcription initiation complex and preventing elongation by RNA polymerase. Because it can bind DN… (More on Actinomycin)