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Promoter: Promoters are used to drive the transcription of the vector's transgene as well as the other genes in the vector such as the antibiotic resistance gene. Some cloning vectors need not have a promoter for the cloned insert but it is an essential component of expression vectors so that the cloned product may be expressed.
A promoter is induced in response to changes in abundance or conformation of regulatory proteins in a cell, which enable activating transcription factors to recruit RNA polymerase. [3] [4] Given the short sequences of most promoter elements, promoters can rapidly evolve from random sequences.
Promoter activity is a term that encompasses several meanings around the process of gene expression from regulatory sequences —promoters [2] and enhancers. [3] Gene expression has been commonly characterized as a measure of how much, how fast, when and where this process happens. [ 4 ]
The Inr element for core promoters was found to be more prevalent than the TATA box in eukaryotic promoter domains. [9] In a study of 1800+ distinct human promoter sequences it was found that 49% contain the Inr element while 21.8% contain the TATA box. [9] Out of those sequences with the TATA box, 62% contained the Inr element as well.
The promoters used for these vector are usually based on the promoter of the lac operon or the T7 promoter, [11] and they are normally regulated by the lac operator. These promoters may also be hybrids of different promoters, for example, the Tac-Promoter is a hybrid of trp and lac promoters. [12]
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]
The Pribnow box has a function similar to the TATA box that occurs in promoters in eukaryotes and archaea: it is recognized and bound by a subunit of RNA polymerase during initiation of transcription. [3] This region of the DNA is also the first place where base pairs separate during prokaryotic transcription to allow access to the template strand.
The promoter gene is turned on (transcribed) when the target agent is present in the cell’s environment. The promoter gene in a normal bacterial cell is linked to other genes that are then likewise transcribed and then translated into proteins that help the cell in either combating or adapting to the agent to which it has been exposed.