Question

Why do methylated cytosines produce hotspots for mutation?

What is a trinucleotide repeat and why is it a hotspot for mutation? What is a TNRE? What are some of the human diseases caused by TNREs? Which codon (and which amino acid) are usually involved in these repeats?

Answer 1

Methylated cytocine is generated after the post trascriptional modification which is highly mutation prone site. Due to the high rate of spontaneous deamination of methylated cytocine to thymine results in mismatch of G/T. it is a hotspot for mutation.

Tri nucleotide repeat is simple called as a CpG island, in which the region of DNA has repeated C and G subunits. Here in CpG island one cytocine base is methylated hence it leads to continues spontaneous deamination of methylated cytocine to thymine. It is occurs 1 into 10⁷ cytosine base per day. Results in G to T mismatch.

TNRE stand for Tri Nucleotide Repeat Expansion. Huntington’s disease, spinocerebellar atexia and fragile X are common type of triple repeat expansion disorders.

CAG codon is generally involve in TNRE and which is code for glutamine