In article <1993Mar8.182657.1 at msscc.med.utah.edu> ctwittwer at msscc.med.utah.edu writes: >Exonuclease III from E. coli won't touch a 3' overhang. I'd like to use an >exo which won't touch a 5' overhang. This may not be quite what you are looking for, but ExoIII will not "touch" a 5' overhang that has been filled in (Klenow) with thio-dNTPs.