Sigma factor: Difference between revisions

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== Overview ==

'''Sigma (σ) factor''' is the peoptide subunit needed for the initiation of RNA transcription in prokaryotic organisms. As opposed to eukaryotes, who utilize a variety of proteins to initiate gene transcription, ~~prokaryotes only use the~~ σ-factor. The large and biologically essential protein, RNA polymerase (RNAP), contains one σ-subunit, which binds <scene name='59/591940/Dna_promoter/1'>Promoter Sequences</scene>, located upstream of transcription start sites.

'''Sigma (σ) factor''' is the peoptide subunit needed for the initiation of RNA transcription in prokaryotic organisms. As opposed to eukaryotes, who utilize a variety of proteins to initiate gene transcription, prokaryotic transcription is initiated almost completely by a σ-factor. The large and biologically essential protein, RNA polymerase (RNAP), contains one σ-subunit, which binds <scene name='59/591940/Dna_promoter/1'>Promoter Sequences</scene>, located upstream of transcription start sites.

== Specific Function and Structure ==

The '''σ-factor''' performs two chief functions: to direct the catalytic core of RNAP to the +1 start site of transcription, and finally to assist in the initiation of strand seperation of double-helical DNA, ultimately forming the transcription "bubble."

The '''σ-factor''' performs two chief functions: to direct the catalytic core of RNAP to the +1 start site of transcription, and finally to assist in the initiation of strand seperation of double-helical DNA, ultimately forming the transcription "bubble." Each gene promoter utilizes a specific promoter region about 40 bp upstream of the transcription start site, and therefore different σ-factors play a role in the regulation of different genes.

===Domains===

Each σ is composed of a variable number of structured domains. The simplest σ-factors have two domains, few have three, and others, called '''housekeeping σ-factors''' have 4 domains. Each of these domains has DNA-binding determinants, or motifs that recognize specific sequences and conformations in DNA. Most commonly, these recognized motifs occur at the -35 and -10 locations upstream of the +1 site.

== Relevance ==

Sigma factor: Difference between revisions

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 == Overview ==
-'''Sigma (σ) factor''' is the peoptide subunit needed for the initiation of RNA transcription in prokaryotic organisms.  As opposed to eukaryotes, who utilize a variety of proteins to initiate gene transcription, prokaryotes only use the σ-factor.  The large and biologically essential protein, RNA polymerase (RNAP), contains one σ-subunit, which binds <scene name='59/591940/Dna_promoter/1'>Promoter Sequences</scene>, located upstream of transcription start sites.
+'''Sigma (σ) factor''' is the peoptide subunit needed for the initiation of RNA transcription in prokaryotic organisms.  As opposed to eukaryotes, who utilize a variety of proteins to initiate gene transcription, prokaryotic transcription is initiated almost completely by a σ-factor.  The large and biologically essential protein, RNA polymerase (RNAP), contains one σ-subunit, which binds <scene name='59/591940/Dna_promoter/1'>Promoter Sequences</scene>, located upstream of transcription start sites.
 == Specific Function and Structure ==
-The '''σ-factor''' performs two chief functions: to direct the catalytic core of RNAP to the +1 start site of transcription, and finally to assist in the initiation of strand seperation of double-helical DNA, ultimately forming the transcription "bubble."
+The '''σ-factor''' performs two chief functions: to direct the catalytic core of RNAP to the +1 start site of transcription, and finally to assist in the initiation of strand seperation of double-helical DNA, ultimately forming the transcription "bubble."  Each gene promoter utilizes a specific promoter region about 40 bp upstream of the transcription start site, and therefore different σ-factors play a role in the regulation of different genes.
+===Domains===
+Each σ is composed of a variable number of structured domains.  The simplest σ-factors have two domains, few have three, and others, called '''housekeeping σ-factors''' have 4 domains.  Each of these domains has DNA-binding determinants, or motifs that recognize specific sequences and conformations in DNA.  Most commonly, these recognized motifs occur at the -35 and -10 locations upstream of the +1 site.
 == Relevance ==