In eukaryotic cells, transcription cannot begin until _____

 In eukaryotic cells, transcription cannot begin until _____

A. sigma binds to the -10 and 35 boxes

B. several basal transcription factors have bound to the promoter

C. the 5′ caps are removed from the mRNA

D. the DNA introns are removed from the template

E. DNA nucleases have isolated the transcription unit

Answer: B. several basal transcription factors have bound to the promoter

Transcription in eukaryotic cells cannot start until several basal transcription factors bind to the promoter region of a gene. This contrasts with prokaryotic transcription, for which a single sigma factor is sufficient to initiate transcription.

The basal transcription factors in eukaryotes are TFIID, TFIIB, TFIIF.TFIIE and others. The TATA box in the promoter is first bound by the factor, TFIID. This makes the DNA fold thus providing room for attachment of other factors. RNA polymerase II binds TFIIB. TFIIF helps in promoter recognition and RNA polymerase II recruitment. TFIIE unravels the DNA double helix. TFIIH has helicase activity to continue the unwinding of DNA. When all these conditions are met, having formed the preinitiation complex at this point RNA polymerase II can then bind and initiate transcription. Thus, without the necessary assembly of basal transcription factors on the promoter, pol II cannot bind with DNA template and it cannot initiate.