Formation of pre-initiation complex with Pol I and Pol III | Expression of Gene : Protein Synthesis Transcription in Prokaryotes and Eukaryotes | Genetics, Biotechnology, Molecular Biology, Botany

⇒	Expression of Gene : Protein Synthesis 2. Transcription in Prokaryotes and Eukaryotes
⇒	Transcription in prokaryotes
	⇒	Single RNA polymerase in E. coli
	⇒	Promoter sites for initiation of transcription in prokaryotes
	⇒	Initiation and elongation of RNA synthesis in prokaryotes
	⇒	'Inchworm model' for elongation of transcript
	⇒	Elongation arrest vs termination of transcription
	⇒	Termination and antitermination of mRNA synthesis in prokaryotes
⇒	Transcription in eukaryotes
	⇒	Multiple RNA polymerases in eukaryotes
	⇒	Promoter, enhancer and silencer sites for initiation of transcription in eukaryotes
	⇒	Transcription factors and initiation of RNA synthesis in eukaryotes
	⇒	Formation of preinitiation (transcription) complex with RNA polymerase II (Pol II)
	⇒	Structure and role of TFIID and other transcription factors (TBP, TAFs)
	⇒	TFIIB domains for interaction with TFIID/TATA complex
	⇒	Phosphorylation of CTD of a subunit of Pol II
	⇒	Formation of pre-initiation complex with Pol I and Pol III
	⇒	Separate DNA binding and transcription activation domains
	⇒	Transcription factors and elongation of RNA chains in eukaryotes
⇒	Chromatin structure and transcription
⇒	Transcription in mitochondria
	⇒	Transcription of vertebrate mtDNA
	⇒	Transcription of yeast and plant mtDNA
⇒	Transcription in chloroplasts

Formation of pre-initiation complex with Pol I and Pol III
For the initiation of transcription at genes transcribed by RNA polymeTare I (Pol I) and RNA polymerase III (Pol III), only one transcription factor each (TIFI and TFIIIB respectively), bound upstream, is needed for directing the RNA polymerase enzyme to its binding site (promoter). However, assembly factors may be needed for mediating the binding of transcription initiation factor. Therefore, following two types of frans-acting protein factors are needed for initiation by Pol I and Pol III : (i) assembly factors and (ij) initiataion factors. For RNA polymerase I (Pol I), the need for assembly factor (UBF) is not obligatory, but is species dependent. However, in Xenopus laevis, for RNA polymerase III (Pol III), two assembly factors (TFIIIA and TFIIIC) in case of 5S RNA genes and one assembly factor (TFIIIC) for tRNA genes are needed to mediate the binding of transcription initiation factor, TFIIIB. These assembly factors can be removed, after binding of the initiation factor without any effect on subsequent transcription (5S RNA is an example). Role of initiation and assembly factors for Pol I and Pol III is shown in Fig 32.19.

Use of transcription assembly factors (hatched) and transcription initiation factors (solid black) for binding of RNA polymerase I (Pol I) and RNA polymerase III (Pol III).

Fig. 32.19. Use of transcription assembly factors (hatched) and transcription initiation factors (solid black) for binding of RNA polymerase I (Pol I) and RNA polymerase III (Pol III).


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