The structure of a eukaryotic transcription complex contains many more transcription factors than a prokaryotic transcription system. These proteins are needed to recognize the specific DNA sequences in the eukaryotic promoter to which RNA polymerase binds to initiate transcription.
The transcription complex positions RNA polymerase at the beginning of a eukaryotic gene. The complex contains basal factors, such as the TATA-binding proteins. The RNA polymerase requires multiple transcription factors to form the transcription complex that recognizes specific sequences such as the "TATA" box that precedes the start site for pre-mRNA synthesis.