Poly(dG)–poly(dC) DNA appears shorter than poly(dA)–poly(dT) and possibly adopts an A-related conformation on a mica surface under ambient conditions

Three types of DNA: ∼2700 bp polydeoxyguanylic olydeoxycytidylic acid [poly(dG)–poly(dC)], ∼2700 bp polydeoxyadenylic polydeoxythymidylic acid [poly(dA)–poly(dT)] and 2686 bp linear plasmid pUC19 were deposited on a mica surface and imaged by atomic force microscopy. Contour length measurements show that the average length of poly(dG)–poly(dC) is ∼30% shorter than that of poly(dA)–poly(dT) and the plasmid. This led us to suggest that individual poly(dG)–poly(dC) molecules are immobilized on mica under ambient conditions in a form which is likely related to the A-form of DNA in contrast to poly(dA)–poly(dT) and random sequence DNA which are immobilized in a form that is related to the DNA B-form.