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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.
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]
The initiating nucleotide of bacterial transcripts bears a 5′ triphosphate (5′-PPP), which can be used for genome-wide mapping of transcription initiation sites. [ 35 ] In archaea and eukaryotes , RNA polymerase contains subunits homologous to each of the five RNA polymerase subunits in bacteria and also contains additional subunits.
Initiation of translation in bacteria involves the assembly of the components of the translation system, which are: the two ribosomal subunits (50S and 30S subunits); the mature mRNA to be translated; the tRNA charged with N-formylmethionine (the first amino acid in the nascent peptide); guanosine triphosphate (GTP) as a source of energy, and the three prokaryotic initiation factors IF1, IF2 ...
Abortive initiation is a normal process of transcription and occurs both in vitro and in vivo. [2] After each nucleotide-addition step in initial transcription, RNA polymerase, stochastically, can proceed on the pathway toward promoter escape (productive initiation) or can release the RNA product and revert to the RNA polymerase-promoter open complex (abortive initiation).
Bacterial transcription is governed by three main sequence elements: Promoters are elements of DNA that may bind RNA polymerase and other proteins for the successful initiation of transcription directly upstream of the gene. Operators recognize repressor proteins that bind to a stretch of DNA and inhibit the transcription of the gene.
Mechanism for transcription initiation at the TATA box. Transcription factors, TATA binding protein (TBP), and RNA polymerase II are all recruited to begin transcription. The TATA box is a component of the eukaryotic core promoter and generally contains the consensus sequence 5'-TATA(A/T)A(A/T)-3'. [3]
This switch helps to regulate the affinity of the ribosome for the initiation factor. [2] The bacterial 30S initiation complex, [7] also showing the Shine-Dalgarno sequence upstream of the start codon. A eukaryotic initiation factor eIF3 plays an important role in translational initiation. It has a complex structure, composed of 13 subunits.