Figure 3.

Influence of DNA conformational elements on solvent accessibility within the major groove. The directional change (Inc, increase; Dec, decrease) for each of the six dinucleotide step parameters that yields an increased ASA_N7 for the central guanine base is shown for idealized GGG trinucleotides (entailing a 5′ and a 3′ GG dinucleotide step). The ‘canonical’ reference point has values of 35° for twist, 3.3 Å for rise and 0 for the remaining four step parameters. The ‘+’ and ‘−’ symbols indicate the general conformational coupling that occurs in real DNA; shift and tilt are positively correlated, whereas roll is anti-correlated with twist and slide. With consideration of this coupling, parameters on either the 5′ or 3′ side that cannot work in a cooperative fashion with either shift or roll to elevate ASA_N7 are indicated with arrows in green.