Relative stabilities of N analogues (black), N′ analogues (blue), and AFF constructs (red) determined by thermal denaturation. Empty and filled symbols indicate the absence and presence of 1 mM ribose, respectively. Lines are drawn to guide the eye only: (A) N60, N′60, and AFF60, (B) N70, N′70, and AFF70, (C) N186, N′186, and AFF186, and (D) N210, N′210, and AFF210.