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The process of transcription can be stopped in prokaryotes in two different ways: factor-independent and factor-dependent. There are specific sequences of DNA that serve as signals to the RNA polymerase, telling it to stop the transcription process. An inverted repeat and an adjacent string of uracils were both encoded in the DNA that made up a terminator sequence. In the process of factor-dependent termination, a terminator sequence is required, in addition to a factor or protein known as rho. There is a lack of understanding regarding the mechanisms that eukaryotes use to terminate transcription. The majority of eukaryotic genes are transcribed for a period of time that extends beyond the actual end of the gene by up to several thousand base pairs. When the RNA is processed further into its mature form, the surplus RNA is subsequently cleaved off of the transcript.
Abstract
In HeLa nuclear extracts, when transcription is coupled to pre-mRNA processing, nascent transcripts become attached to RNA polymerase II during assembly of the cleavage/polyadenylation apparatus (CPA). These nascent transcripts are not released even after being cleaved at the poly(A) site. Here, we show that these cleaved transcripts are anchored to the polymerase at their 3′ ends by the CPA or, when introns are present, by the larger 3′-terminal exon definition complex (EDC), which is composed of splicing factors complexed with the CPA. Both of these complexes are composed of splicing factors. When the RNA is only held in place by the CPA, the addition of Poly(A) allows the RNA to be freed from the polymerase. Poly(A) addition continues to be necessary when anchored by the EDC; however, it does not initiate release until after it has been licensed by splicing. The process by which RNA must first be attached to the polymerase by the EDC, and then can only be released following dual inputs from splicing and polyadenylation, provides an obvious opportunity for surveillance as the RNA enters the transport pathway. This is because the RNA can only be released following the dual inputs from splicing and polyadenylation.
Processing of RNA
cotranscriptional processing, release of transcripts, poly(A) signal, cleavage and polyadenylation, splicing, exon definition complex and coupling are some of the keywords that can be associated with this topic.
Initiation
DNA sequences known as promoters are responsible for directing the beginning of the transcription process. They do this by informing the RNA polymerase enzyme where to start the transcription process. The subunits that enable RNA polymerases to recognise and bind promoters are called initiation factors. It is possible for a purine or a pyrimidine to act as the initiating nucleotide. There are many different eukaryotic promoters, each of which contains a number of different promoter sequence elements. Some of the elements determine the frequency with which transcription is initiated at a particular gene, while others specify where transcription is to be initiated or where it is to be initiated at all. The initiation of transcription in eukaryotes is complicated and involves numerous factors (proteins) that must interact with the DNA and with one another to initiate transcription.
Promoters
Only one strand of the DNA that encodes a gene, a regulatory sequence, or a promoter needs to have a copy made into a molecule.
Since the strand of DNA that is written is the one that is identical to the RNA transcript, the antisense strand of DNA is always selected for presentation because it is the one that is written.
The first base on the DNA that is located at the location where transcription actually begins is denoted by the number 1.
Negative numbers are assigned to the sequences that come before the first base of the transcript and are considered to be upstream of it. The sequences that come after the first base of the transcript, which are considered to be downstream, are given positive numbers as labels.
Conclusion
A core element that is approximately 70 base pairs long and an upstream element that is approximately 100 base pairs long make up the RNA pol I promoter. The core is composed of sequences that are located both upstream and downstream of the initiation site in the DNA. It spans a segment of DNA.
