Elementary Steps of Eucaryotic Transcription

As in procaryotes, the elementary steps of initiation, elongation and termination can be distinguished in eucaryotic transcription. Aside from the specific RNA polymerases, transcription in eucaryotes requires the action of numerous other proteins which are collectively known as transcription factors. Transcription factors are required at the level of initiation, elongation, and termination and are accordingly known as initiation factors, elongation factors and termination factors of transcription. 

Transcription in eucaryotes can, as shown schematically in Fig. 1.31, be subdivided in the following steps (Review Roeder, 1996, Nikolov and Burley, 1997)  

Transcription is regulated to a great deal at the start of transcription, i.e. steps (1-4). These steps are thus the center point of the following discussion. One must keep in mind that in vivo transcription does not occur on naked DNA, but rather on chromatin, i.e. nucleosome-coated DNA. Activation of transcription requires an active remodeling of the chromatin structure at the transcription start sites and within the transcribed regions. Every discussion of the individual steps of transcription must consider this fact. However, only incomplete in vitro systems are available for the study of transcription of chromatin-associated DNA, so that in the following discussion only the data on the transcription of naked DNA is presented. 

Promotor selection, binding of basal initiation factors Binding of the RNA polymerase II Formation of a basal transcription apparatus 

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