Leader sequence

Leader sequence is a nucleotide sequence at the 5' end of an mRNA molecule. It is also known as the 5' untranslated region (5' UTR). This region is important in the regulation of gene expression, as it contains elements that influence the efficiency of translation.

Function

The leader sequence plays a crucial role in the initiation of protein synthesis. It is the site where the ribosome binds to the mRNA molecule to start translation. The leader sequence also contains regulatory elements, such as ribosome binding sites and Shine-Dalgarno sequences, which influence the efficiency of translation.

In some cases, the leader sequence can also regulate gene expression through a mechanism known as attenuation. This involves the formation of secondary structures in the mRNA molecule that can either promote or inhibit translation.

Structure

The structure of the leader sequence varies among different organisms and genes. In prokaryotes, the leader sequence typically contains a Shine-Dalgarno sequence, which is a purine-rich sequence that pairs with a region in the small ribosomal subunit to facilitate ribosome binding.

In eukaryotes, the leader sequence is usually longer and more complex. It may contain cap structures, Kozak consensus sequences, and other elements that influence translation.

Examples

One well-studied example of a leader sequence is the trp operon in Escherichia coli. The leader sequence of this operon contains an attenuator that regulates the expression of the downstream genes in response to the availability of tryptophan.

Another example is the iron-responsive element (IRE) in the leader sequence of the ferritin mRNA in humans. The IRE binds to an iron-responsive element-binding protein (IRE-BP) in the absence of iron, preventing translation. When iron is present, the IRE-BP dissociates, allowing translation to proceed.