Which feature of the major groove enables sequence-specific protein binding?

• A. It is inaccessible and always prevents protein binding.
• B. RNA polymerase binds exclusively there.
• C. DNA methylation occurs at the major groove.
• D. It provides accessible sequence-specific information that transcription factors read.

Answer: (D)

Proteins recognize DNA by reading the pattern of chemical features exposed by base pairs, especially in the major groove. The major groove presents a larger, more accessible surface with distinct hydrogen-bond donors and acceptors that vary with the particular base pair sequence. This creates a readable code that transcription factors and other DNA-binding proteins can “read” to distinguish one sequence from another. That sequence-specific readout is precisely what enables targeted binding to specific DNA motifs, driving precise regulation of gene expression.

The other ideas miss this key point: the major groove is not inaccessible—proteins commonly bind there; RNA polymerase is not restricting binding to only the major groove; methylation can occur in or near the major groove but is not the feature that enables the sequence-specific readout by transcription factors.