General initiation factors

The TATA box and/or an initiation sequence are structural elements which define a minimal promoter from which in vitro transcription can be initiated. A classical TATA box is often, though not always, ca. 30bp from the transcription start site. The initiation sequence includes sequences in the immediate vicinity of the transcription start site. The TATA box and initiation sequence are sufficient for the formation of a basal transcription apparatus composed of general initiation factors for transcription and RNA polymerase II (see Fig. 1.31). 

Formation of a Basal Transcription Apparatus from General Initiation Factors and RNA Polymerase... 

In contrast to the procaryotes, where the o -holoenzyme of the RNA polymerase can initiate transcription without the aid of accessory factors, the eucaryotic RNA polymerase requires the help of numerous proteins to begin transcription. These proteins are termed basal or general initiation factors of transcription. Together with RNA polymerase II, they participate in the basal transcription apparatus. The various components must associate in a defined order for the formation of a transcription-competent complex, from which a low level of transcription is possible. An increase in the basal transcriptional level requires the effect of specific transcriptional activators, which bind cognate DNA sequences at a variable distance from the promoter. The transcriptional activators themselves require the aid of further protein factors, known as coactivators (see 1.4.3.2), in order to attain full stimulatory activity. 

The purification and structural and functional characterization of the general initiation factors has proven extremely difficult. The specific function of the various factors, as well as their structural role in the entire complex, remains poorly resolved. According to the current model, the general transcription initiation factors, with which an exact start of transcription is possible in vitro, are required for the formation of a basal... 

Table 1.L General initiation factors of transcription by RNA polymerase II After Roeder (1996). TAF TATA box binding protein associated factor TBP TATA box binding protein RNA Pol II RNA polymerase II...

The formation of an active, regulation-competent initiation complex for transcription in eucaryotes demands the concerted action of a large number of proteins. It is estimated that more than 50 different proteins participate in the initiation of transcription in eucaryotes. The basal transcription complex, consisting of the general initiation factors, as well as RNA polymerase 11, allows only for a slow transcription rate. For a regulated acceleration of this low transcription rate it is necessary to have - apart from the regulatory DNA-binding proteins - mediation by further co-activator proteins. 

Roeder, R.G. The role of general initiation factors in transcription by RNA polymerase II (1996) Trends Biochem. Sd. 21, 327-555... 

In contrast to the procaryotes, where the er70-holoenzyme of the RNA polymerase can initiate transcription without the aid of accessory factors, the eucaryotic RNA polymerase requires the help of numerous proteins to begin transcription. These proteins are termed basal or general initiation factors oftranscription. Together with RNA polymerase... 

Promoter-specific transcription by Pol II, for example, requires at minumun five general initiation factors designated TFIIB, TFIID, TFIIE, TFIIF, and TFIIH with the exception of TFIIB, all are multisubunit... 

Fig. 10.2. The promoter region of a hormone-sensitive eukaryote gene, showing the transcriptional (actors that interact with different elements of the promoter. TF, transcription factor Spl, general initiation factor.

The cases discussed in this and the preceding two sections are clear-cut examples of mRNA competition for a general initiation factor that results in the preferential translation of certain mRNA species... 

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