MBB 331 Lecture 17

What is the purpose of RNA splicing?

To remove introns and join exons to produce mature mRNA.

What are the two untranslated regions in a typical eukaryotic gene?

5' UTR and 3' UTR.

What are exons and introns?

Exons are coding sequences that remain in mature mRNA, while introns are non-coding sequences that are spliced out.

What is the spliceosome?

A complex of proteins and RNA that facilitates the splicing of pre-mRNA.

What are the two types of self-splicing introns?

Group 1 and Group 2 self-splicing introns.

What is the GU-AG rule in splicing?

The rule that the 5' splice site has a GU sequence and the 3' splice site has an AG sequence.

What is a lariat in the context of RNA splicing?

A loop structure formed during the splicing process when the intron is excised.

What is transesterification in RNA splicing?

A reaction where the 2'-OH of a branch site A attacks the 5' splice site, facilitating the splicing process.

What is the role of the invariant A in splicing?

It provides a 2'-OH that is crucial for the transesterification reaction during splicing.

What is the significance of the pyrimidine tract in splicing?

It is a region that helps in the recognition of splice sites by the spliceosome.

How are exons joined during splicing?

Through nucleophilic attacks that break and rejoin the RNA backbone.

What is the order of intron removal in splicing?

It can vary and does not always follow a linear progression.

What are snRNPs?

Small nuclear ribonucleoprotein particles that are components of the spliceosome.

What are the five key snRNPs involved in splicing?

U1, U2, U4, U5, and U6.

What is the role of Serine-Arginine rich (SR) proteins in splicing?

They help select and regulate splice sites in pre-mRNAs.

What happens during the first step of transesterification?

The 2'-OH of the branch site A attacks the phosphate of the 5' splice site.

What is the function of U2AF in splicing?

It is an auxiliary factor that recognizes the acceptor site.

What is the significance of the branch point in splicing?

It marks the location of the 3' splice site and is crucial for the splicing process.

What is the outcome of the splicing process?

The production of a continuous coding sequence in mature mRNA.

What is the consensus sequence for the branch site in yeast?

UACUAAC.

What is the role of U1 snRNP in splicing?

It recognizes the 5' splice site.

What is the role of U2 snRNP in splicing?

It recognizes the branch site.

What is the role of U4, U5, and U6 snRNPs in splicing?

They bring the splice sites together and help catalyze the splicing reactions.

What is a primary transcript?

The initial RNA molecule synthesized from a gene before splicing.

What does the term 'spatiotemporal usage' refer to in splicing?

The specific selection of splice sites based on the spatial and temporal context of RNA.

What is the significance of the conserved sequences in introns?

They mark the boundaries of exons and introns for the spliceosome.

What is the main focus of the lecture on RNA splicing?

Understanding the nuclear pre-mRNA splicing system in higher eukaryotes.

What is the role of U1 in RNA splicing?

U1 binds to the 5' splice site (GU) and is essential for spliceosome assembly.

What does U2AF bind to during RNA splicing?

U2AF binds to the 3' splice site (AG) and recruits U2.

What is the function of U2 in the splicing process?

U2 binds to the branch point of the intron.

What type of interaction occurs between U1 snRNA and the donor site?

An RNA-RNA interaction due to base pairing.

What is the role of the branch-binding protein (BBP) in splicing?

BBP binds to the branch site before being displaced by U2 snRNP.

What happens during the first step of splicing?

U1 binds to the GU site, recognizing the intron.

What is the composition of U1 snRNP?

U1 snRNP consists of 8 proteins and U1 snRNA.

Why is the base pairing between U1 snRNA and the 5' splice site important?

It is necessary for splicing and spliceosome assembly.

What is the consequence of mutating specific nucleotides in U1 snRNA?

Mutations can inhibit splicing, but compensatory mutations can restore it.

What happens in Stage 2 of splicing?

The U4-U6-U5 trimeric snRNP displaces U1 and brings exons into proximity.

What catalyzes the attack of the 2'-OH of the A residue during splicing?

U6 and U2 catalyze the attack on the phosphodiester bond at the 5' splice site.

What is formed during the cleavage of the donor site?

A lariat-shaped RNA containing the intron and 3' exon is formed.

What is the role of U5 in the splicing process?

U5 bridges the 3' end of Exon 1 and the 5' end of Exon 2.

What happens during the ligation stage of splicing?

The U2-U5-U6 complex catalyzes the joining of the two exons.

What is the function of the 5' cap and 3’ poly(A) tail in splicing?

They influence the splicing of the first and last introns, respectively.

What role does RNA polymerase II (RNAP II) play in splicing?

Phosphorylation of RNAP II CTD aids in the assembly of splicing factors.

What is self-splicing in the context of introns?

Self-splicing introns can catalyze their own removal without the spliceosome.

Who discovered self-splicing introns and in which organism?

Thomas Cech discovered self-splicing introns in the rRNA of Tetrahymena.

What initiates the transesterification reaction in group I introns?

An exogenous guanosine (G) is required to initiate the reaction.

What is the significance of the secondary and tertiary structures of group I introns?

They provide evidence that RNA can have catalytic functions.

What is the role of U4 in the splicing process?

U4 sequesters U6 until it is needed for splicing.

What happens to the lariat formed during splicing?

The lariat is rapidly degraded after splicing is completed.

What is the importance of the consensus branch point sequence in splicing?

It is complementary to a sequence in U2 snRNA and essential for splicing.

How do mutations in the branch point consensus affect splicing?

Mutations can be suppressed by compensatory mutations in U2 snRNA.

What is the overall summary of the splicing process?

U1 binds to the 5' splice site, U2 binds to the branch site, U2AF binds to the 3' splice site, and U5 brings exons together while U2 and U6 catalyze the splicing.