DNA-SEQUENCE CLEAVED BY RESTRICTION ENDONUCLEASE R-ECORI IN ONLY ONE STRAND

Restriction endonuclease EcoRI cuts both strands of the DNA sequence {A figure is presented} generating two separate frayed ends (Hedgpeth et al., 1972). Here it is shown that under standard digestion conditions, the enzyme also attacks the sequence {A figure is presented} but cuts only one strand. The resulting nick is an efficient initiation point for DNA synthesis by Escherichia coli DNA polymerase I, allowing the selective labelling of one strand of the DNA duplex. In buffers of low molarity and high pH (8.5), EcoRI cleaves sequences with the form {A figure is presented} (Polisky et al., 1975). Thus it seems that under both sets of conditions the enzyme recognises the four-base-pair core sequence {A figure is presented} and that its ability to cleave different adjacent phosphodiester bonds varies with pH and ionic strength. © 1979.