Shine-Dalgarno vs. Kozak: Key Differences in Prokaryotic & Eukaryotic Translation Initiation
Shine-Dalgarno is a 4–8-base ribosome-binding sequence in prokaryotic mRNA, aligning the 30S subunit via base-pairing with the 16S rRNA. Kozak refers to the scanning mechanism in eukaryotes where the 40S subunit slides to the first AUG in a GCCACC**AUG**G context.
Students and researchers swap the two because both guide ribosomes to the start codon. Yet they work in opposite kingdoms—Shine-Dalgarno for bacteria, Kozak for everything else—so mixing them can derail an entire cloning project.
Key Differences
Shine-Dalgarno sits ~5–9 nt upstream of the AUG in prokaryotes and is mandatory. Kozak relies on the 5′ cap and a scanning 40S complex, with the consensus sequence surrounding—not preceding—the AUG.
Which One Should You Choose?
Engineering bacteria? Use Shine-Dalgarno: place a strong RBS like GGAGG right before your gene. Expressing a protein in mammalian cells? Insert the Kozak consensus GCCACC**AUG**G and a 5′ cap to boost translation efficiency.
Can I use Shine-Dalgarno in mammalian cells?
No; mammalian ribosomes ignore RBS-like sequences. They require the 5′ cap and Kozak context.
What happens if I delete the Kozak consensus?
Translation drops sharply; leaky scanning or out-of-frame initiation can occur, producing truncated or non-functional proteins.