Which one of the snRNAs given below base pairs with 5' splice site of pre mRNA?
U1
snRNA Base Pairing with 5' Splice Site
The process of removing introns from pre-mRNA to produce mature mRNA is called splicing. This complex process is carried out by a large molecular machine called the spliceosome.
The spliceosome is composed of several small nuclear ribonucleoproteins (snRNPs), which in turn contain small nuclear RNAs (snRNAs) and associated proteins.
Different snRNAs play specific roles in recognizing and interacting with various regions of the pre-mRNA, including the 5' splice site, the 3' splice site, and the branch point.
- The 5' splice site is typically marked by a GU sequence.
- The 3' splice site is typically marked by an AG sequence.
- The branch point is an adenosine residue located upstream of the 3' splice site.
U1 snRNA and the 5' Splice Site
The question asks which snRNA base pairs with the 5' splice site of pre-mRNA. Among the key snRNAs involved in splicing (\(U_1\), \(U_2\), \(U_4\), \(U_5\), and \(U_6\)), \(U_1\) snRNP is the first component to bind to the pre-mRNA during spliceosome assembly. It specifically recognizes and base pairs with the consensus sequence at the 5' splice site.
This initial binding of \(U_1\) snRNP to the 5' splice site is a crucial step in initiating the splicing process and recruiting other snRNPs to form the complete spliceosome.
Let's briefly look at the roles of other options:
- \(U_2\) snRNP binds to the branch point adenosine.
- \(U_5\) snRNP interacts with the sequences at both the 5' and 3' splice sites later in the process, helping to align the exons.
- \(U_4\) and \(U_6\) snRNPs associate together and join the spliceosome; \(U_6\) is involved in the catalytic activity of splicing, base pairing with \(U_2\) and the 5' splice site later, displacing \(U_1\).
Therefore, the snRNA that initially base pairs with the 5' splice site is \(U_1\).
Important Questions from RNA synthesis and processing
Which one of the following statements related to transcription and processing of mRNA is INCORRECT?
Following statements were made with respect to transcription in eukaryotes:
A. RNA polymerase III synthesises mRNAs in the nucleoplasm
B. The target promoter for RNA polymerase III is usually represented by a bipartite sequence downstream of the transcription start site.
C. The assembly factors TFIIIA and TFIIIC assist the binding of the positioning factor TFIIIB at the precise location.
D. TFIIIB is the last factor that joins the initiation complex.
E. Phosphorylated Ser residues in the C-terminal domain (CTD) of RNA polymerase II serve as binding sites for mRNA processing enzymes.
Which one of the following options represents the correct combination of the statements?
Following statements were made about the post-transcriptional processing of RNA in eukaryotes.
A. Soon after transcription initiation, RNA polymerase II pauses ~30 nucleotides downstream from the site of initiation until the Cap structure is added to the 5' end of the nascent pre- mRNA.
B. The 5' splice sites are functionally divergent whereas the 3' sites are functionally equivalent.
C. In addition to helping in recognition of the splice sites, the exon definition also functions as a splicing regulator by allowing pairing and linking of adjacent 5' and 3' splice sites.
D. The intron definition mechanism applies only to the larger introns (above 500 nucleotides length) and assists in achieving alternate splicing.
E. The splicing reactions carried out in vitro have revealed that the first and second transesterification reactions are reversible.
Which one of the following combination of statements is correct?
Which one of the following statements is NOT a correct feature of Escherichia coli RNA polymerase?
The following statements are related to transcription in bacteria/eukaryotes.
A. During concurrent promoter sequence recognition and melting, melting commences with base flipping where two bases are flipped out into pockets of the primary sigma factor
B. Binding of α-amanitin to RNA polymerase Il permits entry of nucleotides into RNA pol II active site and synthesis of RNA, but prevents translocation
C. RNA polymerase I can use upstream promoters with 3 consensus sequences, as well as internal promoters having a bipartite structure
D. FACT is associated with RNA polymerase during transcriptional elongation and helps displace histone octomers during transcription
Which of the following combinations of statements represents all correct statements?
