Interaction of transcription factors with DNA

(a) The major and minor grooves of DNA result from the helical twist of the antiparallel DNA strands. (b) Functional groups of nitrogenous bases extend into the major groove. The green highlighting shows a hydrogen bond acceptor. Yellow is a hydrogen bond donor. Blue represents a methyl group, and red is a hydrogen atom. (c) The interaction of a transcription factor with DNA depends on multiple weak interactions between amino acid side chains and functional groups of the nitrogenous bases. (d) Functional groups within the major groove define a code that denotes sequence-specific binding by transcription factors; two sequences are shown: 5?–CATGCATG–3? is a sequence found in the promoters of seed-storage protein genes in many plants; 5?–TCCTAATCCC–3? is a sequence found in some Drosophila promoters that is recognized by the bicoid transcription factor.