Dear List, I have a really basic question. For the Corning GAPS slides, where the initial interaction (after printing) between the nucleotide and the slide surface is Ionic. Which covalent bonds are formed after irradiating with UV? I have read two different explanations, one the covalent bonds are between U or T and the amines of the slide surface, second 3' or 5' of the nucleotides form covalent bonds with the amines on the slide. I would appreciate your expert explanation, and if you could point me to a ref. Thanks. Sohail Khan Scientific Programmer COLD SPRING HARBOR LABORATORY Genome Research Center 500 Sunnyside Boulevard Woodbury, NY 11797 (516)422-4076