The cytosine residues in the DNA are methylated at specific di- or tri-nucleotide sequences. Which among these methylation motifs is predominantly…
The cytosine residues in the DNA are methylated at specific di- or tri-nucleotide sequences. Which among these methylation motifs is predominantly found in case of protein-coding genes in animals? (H stands for A, T or C)
Select an option to attempt
Correct Answer: Option A
Explanation
CpG DNA methylation in animals:In animals (especially mammals), DNA methylation occurs almost exclusively at CpG dinucleotides, where cytosine is methylated at the C5 position by DNMT enzymes:• DNMT3A/3B: de novo methylation• DNMT1: maintenance methylation (copies methylation patterns after replication)Functional implications in protein-coding genes:• CpG islands in gene promoters are typically unmethylated in actively transcribed genes.• Methylation of CpG islands in promoters recruits methyl-CpG binding proteins (MBDs) and HDACs, leading to chromatin compaction and gene silencing.• Gene body methylation (in exons) is actually associated with active transcription and prevents spurious transcription initiation.Contrast: In plants, CpHpG and CpHpH are additionally methylated (see Q4).Answer: CpG (Option 1).