Chapter 19 - RNA splicing and Processing Flashcards
There is very little mRNA processing in prokaryotes, so the primary transcript is considered a
mature mRNA
The primary transcript of a eukaryotic gene has the same organization as the gene and is called a
pre-mRNA
A eukaryotic pre-mRNA is usually … before export as a mature mRNA
capped, poly-A tailed, and spliced
Enzymes for capping, tailing, and splicing are coupled to
the transcriptional apparatus
The capping enzymes help the transcriptional apparatus
clear the promoter
TFIIH phosphorylates CTD Ser5 residues during
transition to elongation
Capping enzymes binds to
Ser5-P CTD
Elongating RNAP II associates with enzymes that phosphorylate
Ser2
Some splicing and tailing enzymes bind the
Ser2/5-P CTD
The first nucleotide in an RNA transcript is usually a
purine nucleotide triphosphate
what is the mammalian enzyme responsible for adding the cap
guanylyl-transferase
what enzyme then adds a single methyl group at the 7’ position of the terminal guanine
guanine - 7 - methyltransferase
RNAP II pauses 30 nt downstream of initiation site and
waits for capping enzymes to act
Uncapped nascent RNA is vulnerable to attack by
exonucleases
Cap is also necessary for
initiation of splicing and cytoplasmic export
Most splice sites contain
short consensus sequences
major introns are also known as
U2-type
GU-AG introns
minor introns are also known as
U12-type introns
Differences in the 5’ and 3’ splice site consensus sequences gives the splice sites
directionality
Splice sites are recognized in a
pairwise manner
splice sites are
generic
the splice site apparatus is … in every tissue
the same
splicing is temporarily coupled to
transcription
branch point
Not well conserved in multicellular eukaryotes
Preferences for purines and pyrimidines at each position
Highly conserved target adenine nucleotide
Lies 18-40 nt upstream of the 3’ splice site
Identifies the nearest 3’ splice site for interactions with a 5’ splice site