Illustration of the transcription initiation complex from the vaccinia poxvirus. Unlike other viruses, poxviruses do not use their host cell's machinery to replicate themselves. Instead they replicate in the cytoplasm using their own machinery. Transcription is the synthesis of a complementary strand of mRNA (messenger ribonucleic acid) from DNA (deoxyribonucleic acid, helical, pink). mRNA is the intermediary between DNA and its protein product. To initiate transcription the early transcription factor VETFs/l binds to specific sites, known as promoters, on the DNA strand and triggers unwinding of the double helix. This allows the virus-encoded multi-subunit polymerase (vRNAP) to bind to the DNA and initiate transcription.