Differences between translational intiation in prokaryotes and eukaryotes:

Translational initiation in prokaryotes:

1. In the translational initiation in prokaryotes, the association of the small subunit with the mRNA is mediated by base- pairing interaction between the ribosome binding site and the 16S rRNA.
2. Initiating amino acid (met) needs to be formylated, (therefore, two tRNAs for methionine i.e., tRNA fmet and tRNA met are found).
3. Ribosomes enter the mRNA at AUG codon or at nearby Shine-Dalgarno sequence.
4. No initiation factor or co-factors are required for initial contact between ribosome and mRNA.
5. Small ribosomal subunit (30S) can engage mRNA before binding of initiator met-tRNA fmet.
6. At the end of initiation, the 70S initiation complex are found.

Translational initiation in eukaryotes:

1. In the translational initiation in eukaryotes, the small subunit is already associated with an initiator tRNA when it is recruited to the capped 5end of the mRNA.
2. Initiating amino acid (methionine) is not formylated: (only one tRNA for met i.e., tRNAmet is found)
3. Ribosomes enter at the capped 5-end of mRNA and then advance to AUG codon by linear scanning.
4. ATP and a number of protein factors are needed for ribosomes to engage the mRNA.
5. At the end of initiation the 80S initiation complex are found.
6. Small ribosomal subunit (43S) binds stably to mRNA only after initiator met-tRNA has bound.