mRNA Processing: Capping Modification

Polyadenylation is a post-transcriptional modification of eukaryotic mRNAs, which involves the addition of a poly-A tail

Nearly all mRNAs in eukaryotes undergo polyadenylation

Poly-A tails regulate both translation and mRNA stability

Polyadenylation signals consist of an AAUAAA hexanucleotide sequence upstream of the polyadenylation site and a downstream GU-rich element

An endonuclease cleaves the RNA at a CA site near the AAUAAA sequence, and poly-A polymerase adds a poly-A tail of about 200 adenines to the 3’ end

Poly-A binding proteins play a role in transporting mRNAs from the nucleus to the cytoplasm

Poly-A tail length can control mRNA translation

Splicing is the removal of introns from pre-mRNAs to produce mature mRNAs

The discovery of introns in mRNAs in 1977 led to active research on understanding the splicing mechanism

In vitro systems have been used to study splicing reactions by adding pre-mRNAs to nuclear extracts of mammalian cells

Pre-mRNA splicing occurs in two steps: 1) cleavage at the 5’ splice site and joining of the intron to an adenine near its 3’ end, forming a lariat-like structure 2) cleavage at the 3’ splice site and ligation of the two exons, excising the intron as a lariat

Splicing requires consensus sequences at the 5’ and 3’ splice sites, and at the branch point within the intron

Spliceosomes are large RNA-protein complexes that carry out splicing reactions, consisting of five types of small nuclear RNAs (U1, U2, U4, U5, U6) and associated proteins.

Polyadenylation is a post-transcriptional modification of eukaryotic mRNAs, which involves the addition of a poly-A tail

Nearly all mRNAs in eukaryotes undergo polyadenylation

Poly-A tails regulate both translation and mRNA stability

Polyadenylation signals consist of an AAUAAA hexanucleotide sequence upstream of the polyadenylation site and a downstream GU-rich element

An endonuclease cleaves the RNA at a CA site near the AAUAAA sequence, and poly-A polymerase adds a poly-A tail of about 200 adenines to the 3’ end

Poly-A binding proteins play a role in transporting mRNAs from the nucleus to the cytoplasm

Poly-A tail length can control mRNA translation

Splicing is the removal of introns from pre-mRNAs to produce mature mRNAs

The discovery of introns in mRNAs in 1977 led to active research on understanding the splicing mechanism

In vitro systems have been used to study splicing reactions by adding pre-mRNAs to nuclear extracts of mammalian cells

Pre-mRNA splicing occurs in two steps: 1) cleavage at the 5’ splice site and joining of the intron to an adenine near its 3’ end, forming a lariat-like structure 2) cleavage at the 3’ splice site and ligation of the two exons, excising the intron as a lariat

Splicing requires consensus sequences at the 5’ and 3’ splice sites, and at the branch point within the intron

Spliceosomes are large RNA-protein complexes that carry out splicing reactions, consisting of five types of small nuclear RNAs (U1, U2, U4, U5, U6) and associated proteins.