Final answer:
Actinomycin D inhibits transcription by binding to DNA and preventing the movement of RNA polymerase.
Step-by-step explanation:
Actinomycin D is an antibiotic that inhibits transcription by interacting with DNA. It binds to the double-stranded DNA molecule and inserts itself between successive G=C base pairs. This intercalation disrupts the structure of the DNA and prevents the movement of RNA polymerase along the template, effectively blocking transcription.