My Emacs/AUCTeX combination used to automatically replace a single open quote ' with an accent `, as is required by LaTeX. Many machines and .emacs files later, it doesn't do that anymore. I suppose it's an AUCTeX option, but I couldn't find it. (I thought it would be in the Tex Quote AUCTeX customization menu, but no.)
How can I make the single open quote ' automatically replaced by `?