Transcription factors are essential for transcription of both eukaryotic and prokaryotic cells. The fundamental process is the same in both organisms, however it is more complex in eukaryotes in two distinct ways. Firstly, prokaryotes only require the action of a single RNA polymerase enzyme during transcription whereas eukaryotes have different classes of RNA polymerase for each class of gene. Secondly, instead of RNA polymerase binding directly to the promoter sequence in prokaryotes, eukaryotes have to interact with a variety of additional proteins to initiate transcription. Hence eukaryotic transcription is more complex and specific than prokaryotic .