Question

The major histocompatibility complex (MHC) is located on chromosome 6 in humans and contains more than 200 genes with thousands of correspondent proteins. The expression MHC class I molecules on the cell surface is critical for recognition by cytotoxic T lymphocytes (CTL). This recognition event is an immune response that leads to the destruction of cells displaying MHC class I-viral peptide complexes or cells displaying MHC class I-mutant peptide complexes.

Imagine that a mutation occurred in the UTR of the MHC gene. WOuld this mutation affect gene expression? Why or why not?

Answer 1

UTR regions of a gene which are also called Untranslated region are found on both ends of mRNA, 5' as well as 3'. Initially, they may look like just some extra sequences but both of them have an important role in Gene expression.

5'-UTR and 3'-UTR can interact with each other and form a closed loop structure which inhibits translation. The 5'-UTR also plays an important role in initiation of Translation as it interaction with initiation factors.

3'-UTR also have many regulatory regions which plays role in down regulation as well as up regulation of a gene. 3'-UTR contains AU rich elements which are responsible for translation as well as stability of mRNA.

One major role of 3'-UTR is localization as 3'-UTR codes for localization signal and any mutation in this may also result in a protein which is destined for, let say, membrane may end up being sent to an organelle instead.

So keeping in mind the different points, any mutation in UTR of MHC gene will result in affected gene expression as it can affect the initiation, regulation, mRNA stability as well as transportation of MHC molecule to the membrane.