How does DNA methylation influence gene expression?

How does DNA methylation influence gene expression?

• A. Only affects translation, not transcription.
• B. Promotes RNA polymerase error rate.
• C. Generally represses transcription by altering chromatin structure or blocking transcription factor binding.
• D. Increases transcription by loosening chromatin.

Answer: (C)

DNA methylation generally represses transcription by altering chromatin structure or blocking transcription factor binding. When a cytosine in CpG dinucleotides is methylated, it can recruit proteins that promote a closed, compact chromatin state, making the DNA less accessible to RNA polymerase II and other transcriptional machinery. It can also directly hinder transcription factors from binding to their recognition sites if those sites are methylated, further reducing transcription initiation. This modification mainly affects the initiation step of gene expression, not translation, which occurs later in the process. It also doesn’t increase transcription by loosening chromatin; loosening would be associated with demethylation or histone acetylation, not methylation. While methylation in gene bodies can have different associations, promoter methylation is typically linked to reduced transcription, which is why this option best fits the question.

DNA methylation generally represses transcription by altering chromatin structure or blocking transcription factor binding. When a cytosine in CpG dinucleotides is methylated, it can recruit proteins that promote a closed, compact chromatin state, making the DNA less accessible to RNA polymerase II and other transcriptional machinery. It can also directly hinder transcription factors from binding to their recognition sites if those sites are methylated, further reducing transcription initiation. This modification mainly affects the initiation step of gene expression, not translation, which occurs later in the process. It also doesn’t increase transcription by loosening chromatin; loosening would be associated with demethylation or histone acetylation, not methylation. While methylation in gene bodies can have different associations, promoter methylation is typically linked to reduced transcription, which is why this option best fits the question.