Thus, the starting pool of DNA described herein was prepared by PCR using the synthetic oligomer 5'GGG ACG AAT TCT AAT ACG ACT CAC TAT rA GG AAG AGA TGG CGA CAT CTC N40 GT GAC GGT AAG CTT GGC AC 3' (SEQ ID NO 23), where N is an equimolar mixture of G, A, T and C, and where the DNA molecules were selected for the ability to cleave the phosphoester following the target rA. (See FIG. 4A, also.) Selec