The key difference between Shine Dalgarno and Kozak sequence is that Shine Dalgarno sequence is a ribosomal binding site in bacterial and archaeal messenger RNA, while Kozak sequence is a protein translation initiation site in most eukaryotic messenger RNAs.
Shine Dalgarno and Kozak sequence are two consensus sequences that are very important for translation initiation. In molecular biology, translation is the process by which ribosomes in the cytoplasm synthesize proteins after the process of transcription. In translation, an mRNA (messenger RNA) is decoded in a ribosome to produce a specific amino acid chain outside the nucleus. Typically, a ribosome induces the decoding process by facilitating the binding of complementary tRNA anticodon sequences to mRNA codons. Translation proceeds in three stages: initiation, elongation and termination.
CONTENT
1. Overview and Key Difference
2. What is Shine Dalgarno Sequence
3. What is Kozak Sequence
4. Similarities – Shine Dalgarno and Kozak Sequence
5. Shine Dalgarno vs Kozak Sequence in Tabular Form
6. Summary – Shine Dalgarno vs Kozak Sequence
What is Shine Dalgarno Sequence?
Shine Dalgarno sequence is a ribosomal binding site in bacterial and archaeal messenger RNA. It is generally located around 8 bases upstream of the start codon AUG. This RNA sequence helps in recruiting ribosomes to the messenger RNA by aligning the ribosome with an mRNA start codon. Thus, it initiates protein synthesis. Once after recruitment, the tRNA can add amino acids in sequence as dictated by the mRNA codons. This special sequence is common in bacteria but rarer in archaea. Moreover, it is also present in chloroplast and mitochondrial transcripts. Shine Dalgarno sequence was first proposed by Australian scientists John Shine and Lynn Dalgarno. The six base consensus sequence is AGGAGG. For example, in Escherichia coli the sequence is AGGAGGU.
Figure 01: Shine Dalgarno Sequence
The selection of initiation site (AUG) depends on the interaction between the 30S subunit of ribosome and mRNA template. The pyrimidine rich region on the 16srRNA component of 30S subunit binds to the purine-rich region known as Shine Dalgarno sequence upstream of the AUG initiation codon in mRNA. Furthermore, during the formation of the initiation complex, these complementary nucleotide sequences pair to form a double-stranded RNA structure. This facilitates the binding of mRNA to a ribosome in such a way that the initiation codon is placed at the P site of ribosome.
What is Kozak Sequence?
Kozak sequence is a protein translation initiation site in most eukaryotic mRNA. This sequence is also called the Kozak consensus sequence. Kozak sequence is the optimum sequence for initiating translation in eukaryotes. This sequence is an integral aspect of protein regulation. It is also very important for overall cellular health. It helps correct protein translation from genetic messages by mediating ribosome assembly and translation initiation.
Figure 02: Kozak Sequence
This sequence was named after the scientist who discovered it, Marilyn Kozak. She discovered it through a detailed analysis of DNA genomic sequences. The Kozak sequence is 5’ (gcc) gccRccAUGG-3’. The upper-case letters indicate conserved bases, while lower-case letters indicate common variable bases. R indicates a purine (adenine or guanine) that is always positioned in this location.
What are the Similarities Between Shine Dalgarno and Kozak Sequence?
- Shine Dalgarno and Kozak sequence are two consensus sequences that are very important in translation initiation.
- Both are RNA sequences.
- The smaller subunit of the ribosome binds to both sequences.
- Both sequences mediate the proper ribosome assembly and translation initiation.
- They are integral aspects of protein regulation and overall cellular health.
What is the Difference Between Shine Dalgarno and Kozak Sequence?
Shine Dalgarno sequence is a ribosomal binding site found in bacterial and archaeal messenger RNA, while Kozak sequence is a protein translation initiation site found in most eukaryotic messenger RNA. So, this is the key difference between Shine Dalgarno and Kozak sequence. Furthermore, Shine Dalgarno sequence is 5’AGGAGGU3’ while, Kozak sequence is 5’ (gcc) gccRccAUGG-3’.
The following infographic lists the differences between Shine Dalgarno and Kozak sequence in tabular form for side by side comparison.
Summary – Shine Dalgarno vs Kozak Sequence
Shine Dalgarno and Kozak sequences are two consensus RNA sequences that are very important for ribosome assembly and translation initiation. Shine Dalgarno sequence is a ribosomal binding site in bacterial and archaeal messenger RNA, while Kozak sequence is a protein translation initiation site in most eukaryotic messenger RNA. Thus, this summarizes the difference between Shine Dalgarno and Kozak sequence.
Reference:
1. “Shine-Dalgarno Sequence.” An Overview | ScienceDirect Topics.
2. “Kozak Consensus Sequence.” An Overview | ScienceDirect Topics.
Image Courtesy:
1. “Shine-Dalgarno sequence-es” By Shakiestone. Versión en español de Alejandro Porto – File:Shine-Dalgarno sequence.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Translation regulation by 5’ transcript leader cis-elements” By Apfel412 – Own work (CC BY-SA 4.0) via Commons Wikimedia