What does the Polypyrimidine tract do?
The polypyrimidine tract is a region of pre-messenger RNA (mRNA) that promotes the assembly of the spliceosome, the protein complex specialized for carrying out RNA splicing during the process of post-transcriptional modification.
Where is the Polypyrimidine tract located?
A polypyrimidine tract is typically present between the branch point signal and the splice acceptor site.
Do Spliceosomes catalyze splicing?
Pre-mRNA splicing is catalyzed by the spliceosome, a multimegadalton ribonucleoprotein (RNP) complex comprised of five snRNPs and numerous proteins. Because of its dynamic and complex nature, obtaining structural information about the spliceosome represents a major challenge.
Do Spliceosomes splice exons?
Most splicing occurs between exons on a single RNA transcript, but occasionally trans-splicing occurs, in which exons on different pre-mRNAs are ligated together. The splicing process occurs in cellular machines called spliceosomes, in which the snRNPs are found along with additional proteins.
What is the branch site in splicing?
The branch site is a short motif upstream of the polypyrimidine tract that includes a BP adenosine, in 92% of human BP [3]. During the first step of the splicing reaction the 2’OH of the BP adenosine attacks the first intronic nucleotide (nt) of the upstream 5’ss to form a lariat intermediate [4].
What are the functions of Spliceosomes in RNA splicing?
Abstract. Spliceosomes are multimegadalton RNA–protein complexes responsible for the faithful removal of noncoding segments (introns) from pre-messenger RNAs (pre-mRNAs), a process critical for the maturation of eukaryotic mRNAs for subsequent translation by the ribosome.
What are the five snRNAs involved in splicing reaction?
The spliceosome comprises five snRNAs (small nuclear RNAs), U1, U2, U4, U5 and U6, and many other protein factors.
Why do exons have to be spliced together?
It works by removing introns (non-coding regions of RNA) and so joining together exons (coding regions). For those eukaryotic genes that contain introns, splicing is usually needed to create an mRNA molecule that can be translated into protein.
How does the spliceosome recognize splice junction sequences?
The splice sites are recognized by the splicing machinery based on sequences within the pre-mRNA. Here, we show that the exon sequences at the splice junctions play a significant, previously unrecognized role in the selection of 3′ splice sites during the second step of splicing.
What is the role of the branch point in splicing?
During splicing, the branch point nucleotide initiates a nucleophilic attack on the 5′ donor splice site. The free end of the upstream intron then initiates a second nucleophilic attack on the 3′ acceptor splice site, releasing the intron as an RNA lariat and covalently combining the two exons (53).