Lecture 2 - part one (initiation)

what is needed for the initiation of translation

small ribosomal subunit, capped and polyadenylated mRNA, eIFs, iMET-tRNA, GTP

eIFs

eukaryotic initiation factors

start codon

AUG = methionine

initiating translation process to get to start codon

initiation factor binds to iMET-tRNA

forms a complex with eIF2GTP-tRNA, small subunit of ribosome, and other eIFs to form a 43S complex

mRNA is recruited to the complex, partly due to having IFs associated with the cap - now called the 48S open complex

scanning mRNA for start codon

kozak sequence

the sequence that is conserved around AUG to ensure that AUG is in the correct reading frame

we dont fully know how this is recognised

initiating translation when start codon has been found

when start codon is an P site, tRNA anticodon base pairs with the mRNA start codon

correct base pairing stimulates GTPase activity of eIF so can no longer bind mRNA

large subunit of ribosome binds, all initiation factors come off, another G protein involved

left with ribosome with mRNA, iMET-tRNA in P site and empty A and E sites

initiating translation in prokaryotes

co-transcriptional

requires fMET-tRNA - recognises initiation codon

no 5’ cap on mRNA

Shine-Delgarno sequence directs ribosome to start codon by complimentary sequencing pairing

prokaryotic genes can be

polycistronic