Card Set Information
translation initiation factors...
what subunit & what site of the ribosome does the mRNA & initiator tRNA bind?
small subunit binds mRNA & tRNA
what is a Shine-Dalgarno sequence?
ribosome binding site (RBS) on the mRNA
*the closer it matches the consensus seq. the more efficiently the mRNA will be translated
non-overlapping vs. overlapping genes...
there is a shift of reading frame in overlapping genes (backwards)
non-overlapping has separate SD seq & protein-coding regions
overlapping genes can share SD & protein-coding regions overlap
how does a Shine-Dalgarno seq. work?
SD seq. base pairs w the 3' end of the 16S rRNA subunit of the small ribosomal subunit before the start codon
why are there 2 tRNAs for Met & only 1 codon?
initiator = Met-tRNA^fMet = charged by methionyl-tRNA synthetase, then formyltransferase adds formyl group (H-O=C-) to amide N, so it can only be positioned at the start
Met-tRNA^mMet = internal positions => Met
Prokaryote initiation factors (3)...
function & binding
IF1 - blocks binding of initiator tRNA to A site
IF2 - GTPase that loads initiator tRNA to P site
IF3 - prevents premature binding btwn large & small ribosomal subunits
The 30S binds IF1 & IF3, then mRNA
what causes IF release?
conformational change triggers IF3 release, large subunit binds, GTP hydrolysis cause IF2 release & IF1 releases
...70S Initiation complex
how does translation initiation differ in eukaryotes vs prokaryotes?
- NO SD site, so eIF4e bind 5' end cap
- NO formylation of Met, but still 2 diff tRNAs for initiaton vs internal AUG
Eukaryotic initiation factors (6)...
function & binding
eIF1A (IF1) - blocks A site
eIF1 - blocks E site
eIF3 (IF3) - prevents premature large & small subunit binding
eIF2 (IF2) - GTPase brings Met-tRNA^(i)Met to small subunit
eIF4F complex - mRNA assembly w 43S preinitiation complex
eIF5B - GTPase causes removal of factors allowing 40S + 60S = 80S ribosome