Messenger RNA

Todd MetzgerBMS 265

May 8, 2009

Nomenclature

• Messenger RNAs (mRNA) describes cytoplasmic product

• Pre-mRNA (part of hnRNA) in nucleus is processed and exported

• Describe by gene/protein, including isoform– or NCBI sequence (NM, natural; XM, in silico)– New methods for describing spliced mRNAs

(Sammeth 2008)

1955 - Goldstein and Plaut

6 min

62 hr

Discovery• Volkin and Astrachan discovered a new type

of RNA synthesized following infection of bacteria by T2 Bacteriophage (Volkin 1956)– Newly synthesized RNA mirrored composition of

T2 DNA

• Brenner, Jacob, and Meselson found that only RNA, and not ribosomes, were newly synthesized following infection (1961)– The term messenger RNA was coined

Translation Leads to Linear Protein Synthesis

• Dintzis 1961• Reticulocytes analyzed

– Make ~90% hemoglobin

• Radiolabeled amino acids incorporated to C-terminus only

1970 - Messenger RNA VisualizedMiller et al

Biogenesis

• Enzymatic Reaction by RNA Polymerase– RNA Pol II in eukaryotes

• Involves Initiation Factors (TFIIB,D,E,F,H) and Mediator Complex

• Core RNA polymerase II is 12 subunits, 500 kDA, highly conserved– 10 subunit catalytic core

Woychik 2002, Sims III 2004

Catalytic core

Yeast RNA pol IIPositively charged cleft

Active site occurs between the wall and clamp (shown closed - elongation)

Transcription

• Template DNA, 5 GTFs, and RNA pol II associated to form pre-initiation complex– TFIID contains the TATA-box binding protein (TBP)– TFIIE and -H melt DNA

• CTD phosphorylation is required for dissociation of initiation factors and entrance to the elongation phase

• TFIIS allows stalled transcription to continue– Reverse procession followed by cleaved of RNA

TFIIS

Mediator• Connects transcription factors to basal

machinery

Casamassimi 2007

mRNA Secondary Structure

• Many mRNAs can code for the same protein• Made program to scramble codons while

preserving base content• Looked at 50 bp structures

Katz 2003

mRNA Secondary Structure

- No significant differences for human sequences

mRNA Vaccinations - Direct

Hess et al 2006

mRNA Vaccinations - Indirect

Hess et al 2006