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Bacterial transcription is the process in which a segment of bacterial DNA is copied into a newly synthesized strand of messenger RNA (mRNA) with use of the enzyme RNA polymerase. The process occurs in three main steps: initiation, elongation, and termination; and the result is a strand of mRNA that is complementary to a single strand of DNA.
The number of transcription factors found within an organism increases with genome size, and larger genomes tend to have more transcription factors per gene. [ 14 ] There are approximately 2800 proteins in the human genome that contain DNA-binding domains, and 1600 of these are presumed to function as transcription factors, [ 3 ] though other ...
transcription factor – a substance, such as a protein, that contributes to the cause of a specific biochemical reaction or bodily process; promoter – a region of DNA that initiates transcription of a particular gene; Sigma factor – specialized bacterial co-factors that complex with RNA Polymerase and encode sequence specificity
A sigma factor (σ factor or specificity factor) is a protein needed for initiation of transcription in bacteria. [1] [2] It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase (RNAP) to gene promoters. It is homologous to archaeal transcription factor B and to eukaryotic factor TFIIB. [3]
Additional transcription factors then bind, first TFIIE and then TFIIH. [24] This completes the assembly of the preinitiation complex for eukaryotic transcription. [3] Generally, the TATA box is found at RNA polymerase II promoter regions, although some in vitro studies have demonstrated that RNA polymerase III can recognize TATA sequences. [25]
Cultured mouse embryonic fibroblasts have been found to have roughly 1500 factories through immunofluorescence detection of RNAP II however cells taken from different tissues of the same mouse group had between 100 and 300 factories. [7] Measurements of the number of transcription factories in HeLa cells give a varied result.
A sigma factor is a protein needed only for initiation of RNA synthesis in bacteria. [12] Sigma factors provide promoter recognition specificity to the RNA polymerase (RNAP) and contribute to DNA strand separation, then dissociating from the RNA polymerase core enzyme following transcription initiation. [13]
Several cell function specific transcription factors (there are about 1,600 transcription factors in a human cell [14]) generally bind to specific motifs on an enhancer [15] and a small combination of these enhancer-bound transcription factors, when brought close to a promoter by a DNA loop, govern level of transcription of the target gene.