Time-limited digestion of CMP1 DNA with BAL 31, followed by complete hydrolysis with KpnI. Lane 1, λ DNA hydrolyzed with EcoRI and HindIII; lane 2–5, CMP1 DNA hydrolyzed with BAL 31 followed by KpnI. BAL 31 digestion time: lane 2, 0 min; lane 3, 15 min; lane 4, 30 min; lane 5, 45 min. 1% agarose gel.