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Helicase polarity, which is also deemed "directionality", is defined as the direction (characterized as 5'→3' or 3'→5') of helicase movement on the DNA/RNA single-strand along which it is moving. This determination of polarity is vital in f.ex. determining whether the tested helicase attaches to the DNA leading strand, or the DNA lagging ...
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. [ 1 ] [ 2 ] It consists of RNA polymerase II , a subset of general transcription factors , and regulatory proteins known as SRB proteins [ clarification needed ] .
RNA polymerase II (RNAP II and Pol II) is a multiprotein complex that transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. [ 1 ] [ 2 ] It is one of the three RNAP enzymes found in the nucleus of eukaryotic cells. [ 3 ]
Relieves strain of unwinding by DNA helicase; this is a specific type of topoisomerase DNA ligase: Re-anneals the semi-conservative strands and joins Okazaki Fragments of the lagging strand. Primase: Provides a starting point of RNA (or DNA) for DNA polymerase to begin synthesis of the new DNA strand. Telomerase
The paused transcribing complex has two options: (1) release the nascent transcript and begin anew at the promoter or (2) reestablish a new 3′-OH on the nascent transcript at the active site via RNA polymerase's catalytic activity and recommence DNA scrunching to achieve promoter escape.
At the end of Okazaki fragment synthesis, DNA polymerase δ runs into the previous Okazaki fragment and displaces its 5' end containing the RNA primer and a small segment of DNA. This generates an RNA-DNA single strand flap, which must be cleaved, and the nick between the two Okazaki fragments must be sealed by DNA ligase I.
Transcription preinitiation complex, represented by the central cluster of proteins, causes RNA polymerase to bind to target DNA site. The PIC is able to bind both the promoter sequence near the gene to be transcribed and an enhancer sequence in a different part of the genome, allowing enhancer sequences to regulate a gene distant from it.
There are two problems after leading and lagging strand synthesis: RNA remains in the duplex and there are nicks between each Okazaki fragment in the lagging duplex. These problems are solved by a variety of DNA repair enzymes that vary by organism, including: DNA polymerase I, DNA polymerase beta, RNAse H, ligase, and DNA2.