Question

CpG islands: Which of the following statements is FALSE?

A) MeCP1 and MeCp2 preferentially bind to methylated CpG islands.
B) CpG islands often surround constitutive promoters and are unmethylated normally when the gene is active.
C) MeCp2 recruits HDAC activity to CpG islands as part of the SIN3 repressor complex.
D) pTEFb and Sir3 bind to methylated CpG islands to repress activity.

Answer 1

The false statement among the options provided is that pTEFb and Sir3 bind to methylated CpG islands to repress activity. This is incorrect as pTEFb is involved in transcriptional elongation and Sir3's role is in heterochromatin formation, not in binding methylated CpG islands to repress gene activity.

Step-by-step explanation:

The statement that is FALSE regarding CpG islands is: D) pTEFb and Sir3 bind to methylated CpG islands to repress activity. This statement is false because pTEFb is actually a positive transcriptional elongation factor that aids in the transition from transcription initiation to elongation, rather than binding to methylated DNA to repress activity. On the other hand, Sir3 is a protein associated with gene silencing in yeast, but it does not preferentially bind methylated CpG islands to exert its function. Instead, it is involved with heterochromatin formation and gene silencing at telomeres and mating type loci.

CpG islands are typically found near gene promoters and are usually unmethylated when genes are actively being transcribed. When these islands are methylated, it is often associated with gene repression. Proteins like MeCP1 and MeCP2 do in fact bind to methylated DNA, and the binding of MeCP2 can recruit histone deacetylase (HDAC) activity through the SIN3 repression complex, leading to a more closed chromatin state and gene repression. Therefore, statements A, B, and C are true.