RNA polymerase sigma factor

E. coli has only one RNA polymerase. Sigma factors bind to this RNA polymerase, stimulating its binding to certain sets of promoters, thus simultaneously activating transcription of several operons. The standard sigma factor in E. coli is... 

Carter HL HI, Moran CP. New RNA polymerase sigma factor under SpcO control in BortOus subtits. Proc Natl Acad Sci USA 1986 83 9438-9442. 

Brahamsha B. and Haselkom R. 1992. Identification of multiple RNA polymerase sigma factor homologs in the cyanobacterium Anabaena sp. strain PCC 7120 cloning, expression, and inactivation of the sigB and sigC genes. J Bacteriol 173(8) 2442-50. 

Osanai, T., Numata, K., Oikawa, A., Kuwahara, A., lijima, H., Doi, Y, Tanaka, K., Saito, K., Hirai, M. Y. Increased bioplastic production with an RNA polymerase sigma factor SigE during nitrogen starvation in Synechocystis sp. PCC 6803. DNA Res 2013, 20, 525-535. 

Goff, C. G., Minkley, E. G. The RNA polymerase sigma factor A specificity determinant, p. 124-147. In L. Silvestri (ed.), RNA polymerase and transcription. First Lepetit Colloquium. Amsterdam North Holland 1970. 

The prokaryotic RNA polymerase consists of a core enzyme and an auxiliary protein factor called sigma, (o factor). The core consists of four subunits, two are identical, a, the other two similar, p and P. The P subimit binds the DNA while the p subunit binds the nucleotides that are to be joined together to form the RNA molecule. Sigma factors function in identifying specific DNA sequences known as promoters. Promoters are sites that tell the RNA polymerase where to begin transcription. 

Fig. 2. Modulation of the RseA activity a working model. In the absence of non-native proteins in the periplasm, is bound to the RseA anti-sigma factor this binding is stabilized by RseB, a co-anti-sigma factor, in the periplasm. Upon accumulation of non-native proteins within the periplasm, RseB is released followed by dissociation of which interacts with RNA polymerase core enzyme to initiate transcription of the heat shock genes of the sigma-E regulon...

Template binding RNA polymerase (RNAP) binds to DNA and locates a promoter (P) melts the two DNA strands to form a preinitiation complex (PIQ. (2) Chain initiation RNAP holoenzyme (core + one of multiple sigma factors) catalyzes the coupling of the first base (usually ATP or GTP) to a second ribonucleoside triphosphate to form a dinucleotide. (3) Chain elongation Successive residues are added to the 3 -OH terminus of the nascent RNA molecule. (4) Chain termination and release The completed RNA chain and RNAP are released from the template. The RNAP holoenzyme re-forms, finds a promoter, and the cycle is repeated. 

Colland, F., Fujita, N., Ishihama, A., and Kolb, A. (2002) The interaction between sigmaS, the stationary phase sigma factor, and the core enzyme of Escherichia coli RNA polymerase. Genes Cells 7, 233-247. 

There is a single prokaryotic RNA polymerase that synthesizes all types of RNA in the cell. The core polymerase responsible for making the RNA molecule has the subunit structure Ojpp. A protein factor called sigma (a) is required for the initiation of transcription at a promoter. Sigma factor is released immediately after initiation of transcription. Termination of transcription sometimes requires a protein called rho (p) faaor. This enzyme is inhibited by rifampin. Actinomycin D binds to the DNA preventing transcription. 

Requires sigma (a) to initiate at a promoter No sigma, but transcription factors (TFIID) bind before RNA polymerase... 

With the help of sigma factor, RNA polymerase recognizes and binds to the promoter region. The bacterial promoter contains two consensus sequences, called the Pribnow box (or TATA box) and the -35 sequence. The promoter identifies the start site for transcription and orients the enzyme on the template strand. The RNA polymerase separates the two strands of DNA as it reads the base sequence of the template strand. 

Transcription initiation in procaryotes is controlled via promoters and regulatory DNA sequences located near the promoter. The role of the promoter is to provide a defined association site for the RNA polymerase and to correctly orient it. The binding of the RNA polymerase to its promoter is controlled by the sigma factor, a component of the RNA polymerase holoenzyme. The sigma factor selects which genes are to be transcribed by specifically recognizing the promoter sequence and structure and by allowing the RNA polymerase to form a transcription-competent complex at the transcription start site. 

The RNA polymerase of E. coli possesses with its subimit construction (a2PP o) a simple structure in comparison to eucaryotic RNA polymerases. The sigma factor is only required for the recognition of the promoter and the subsequent formation of a tight complex. After the incorporation of the first 8-10 nucleotides into the transcript, the sigma factor dissociates from the holoenzyme, and the remaining core enzyme carries out the rest of the elongation. 

Holoenzyme The c subunit ( sigma factor") enables RNA polymerase to recognize promoter regions on the DNA. The o subunit plus the core enzyme make up the holoenzyme. [Note Different o factors recognize different groups of genes.]... 

The process of RNA synthesis is called transcription. The enzyme that synthesizes RNA is RNA polymerase, which is a multisubunit enzyme. The core enzyme has four subunits—2 a, 1 p, and 1 p, and possesses 5 —>3 polymerase activity. The enzyme requires an additional subunit—sigma (a) factor—that recognizes the nucleotide sequence (promoter region) at the beginning of a length of DNA that is to be transcribed. Another protein—rho (p) factor—is required for termination of transcription of some genes. 

Describe the role of sigma factors (o) in transcription by prokaryotic RNA polymerases. What is the effect of the release of o from the holoenzyme once transcription has been initiated. How would a mutation that prevents a o factor from dissociating from core RNA polymerase affect the rate of transcription ... 

Alternative Sigma Factors Trigger Initiation of Transcription at Different Promoters Elongation of the Transcript Termination of Transcription Comparison of Escherichia coli RNA Polymerase with DNA Poll and PolIII... 

The enzyme without the sigma factor, called core polymerase, retains the capability to synthesize RNA, but it is defective in the ability to bind and initiate transcription at true initiation sites on the DNA. In fact when RNA polymerase was first purified from crude extracts it was missing the a factor. The assay for polymerase involved the use of DNA with single-strand nicks. When a DNA template was used that did not have single-strand nicks, this enzyme was not active. This led to a search for a missing factor. When this factor (cr70) was added back to the purified core enzyme and the uncut DNA template, the enzyme was able to bind... 

Sigma factor. A subunit of bacterial RNA polymerase that recognizes specific sites on DNA for initiation of RNA synthesis. 

What is the main role of the s (sigma) factor in the E. coli RNA polymerase complex ... 

The RNA polymerase of E. coli contains four subunits, a2PP, which form the core enzyme, and a fifth subunit, the a (sigma) factor, which is required for initiation of RNA synthesis. 

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