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Studies of primary transcripts produced by RNA polymerase II reveal that an average primary transcript is 7,000 nucleotides in length, with some growing as long as 20,000 nucleotides in length. [2] The inclusion of both exon and intron sequences within primary transcripts explains the size difference between larger primary transcripts and ...
RNA polymerase II holoenzyme is a form of eukaryotic RNA polymerase II that is recruited to the promoters of protein-coding genes in living cells. [11] It consists of RNA polymerase II, a subset of general transcription factors , and regulatory proteins known as SRB proteins.
RNA polymerase, assisted by one or more general transcription factors, then selects a transcription start site in the transcription bubble, binds to an initiating NTP and an extending NTP (or a short RNA primer and an extending NTP) complementary to the transcription start site sequence, and catalyzes bond formation to yield an initial RNA product.
RNA Polymerase II Transcription: the process of transcript elongation facilitated by disassembly of nucleosomes. RNAP from T. aquaticus pictured during elongation. Portions of the enzyme were made transparent so as to make the path of RNA and DNA more clear. The magnesium ion (yellow) is located at the enzyme active site.
Transcription elongation is not a smooth ride along double stranded DNA, as RNA polymerase undergoes extensive co-transcriptional pausing during transcription elongation. [30] [31] In general, RNA polymerase II does not transcribe through a gene at a constant pace.
The enzyme RNA polymerase II attaches to the template DNA strand and catalyzes the addition of ribonucleotides to the 3' end of the growing sequence of the mRNA transcript. [9] In order to initiate its function, RNA polymerase II needs to recognize a promoter sequence, located upstream (5') of the gene.
This can initiate messenger RNA (mRNA) synthesis by RNA polymerase II (RNAP II) bound to the promoter at the transcription start site of the gene. The loop is stabilized by one architectural protein anchored to the enhancer and one anchored to the promoter and these proteins are joined to form a dimer (red zigzags).
Polyadenylation is the addition of a poly(A) tail to an RNA transcript, typically a messenger RNA (mRNA). The poly(A) tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In eukaryotes, polyadenylation is part of the process that produces mature mRNA for translation.