Practice question

Genome-wide nucleosome positioning maps reveal sequence features influencing octamer affinity. Experimental SELEX and computational models show DNA sequences where AT-rich minor grooves face inward compress more easily, alternating AT/GC every five base pairs, approximately half helical turn, aligns flexible pyrimidine-purine steps with curvature required around histone, reducing elastic energy cost of wrapping stiff DNA. Poly-A tracts rigid and intrinsically curved disfavor nucleosomes acting as excluding signals, random sequence intermediate, pure GC stretches less bendable. Periodic AT/GC pattern predicts nucleosome occupancy, positioning at promoters and transcription start site depletion, guiding transcriptional regulation across eukaryotic genomes.