CBIO 3400 Lecture Notes - Lecture 6: Transferase, Eukaryotic Translation, 3D Cell Culture
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Exam 4 Lecture 6B- New Lecture Material
mRNA Processing (Splicing Focus)
• We don’t want it immediately degraded.
o So we can translate it, get products from it.
• We also don’t want it to hang around forever.
o Want it to be degraded at some point. don’t want to make certain genes all the
time and waste energy
• We want to precisely control how much and for how long.
o Want to control how much RNA is around and for how long
RNA Pol II CTD: A Very Long Tail That Binds Pre-mRNA Processing Factors
• Enzymes involved in 5' capping, polyadenylation, and splicing bind to the long
phosphorylated CTD of RNA Pol II
• Tail is used in lots of ways as a loading platform
Regulation Starts Before the Message Is Completed
• RNA processing enzymes associate with phosphorylated CTD tail of RNA Pol II (Loaded
on in stages, some in initiation, elongation, and termination)
o Capping Factors
o Splicing Factors
o 3’ End Processing Proteins
What is the 5’ 7-Methyl-G Cap?
• Added after the nascent RNA molecules reach a length of 25-30 nucleotides.
• Guanylyltransferase binds to the Ser5-phosphorylated Pol II CTD and adds GTP.
• As serine 5 is phosphorylated, this serves as a platform for guanyl transferase to
add GTP to nascent mRNA.
• The methyl groups are derived from S-adenosylmethionine.
**5’ 7-Methyl-G Cap is a GTP that’s been added from its 5’ carbon to 5’ carbon on nascent
mRNA. Strange 5’ to 5’ phosphate linkage. Also, modified by methylases.
Functions of 5’ 7-Methyl-G Cap
• Prevents RNA degradation
o Stops nuclease from being able to recognize this.
• Facilitates translation
o Cap serves as binding platform for translation machinery
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