Abstract
The sequence of DNA base pairs adjacent to the phosphodiester bonds cleaved by the RI restriction endonuclease in unmodified DNA from coliphage lambda has been determined. The 5'-terminal nucleotide labeled with (32)P and oligonucleotides up to the heptamer were analyzed from a pancreatic DNase digest. The following sequence of nucleotides adjacent to the RI break made in lambda DNA was deduced from these data and from the 3'-dinucleotide sequence and nearest-neighbor analysis obtained from repair synthesis with the DNA polymerase of Rous sarcoma virus [Formula: see text] The RI endonuclease cleavage of the phosphodiester bonds (indicated by arrows) generates 5'-phosphoryls and short cohesive termini of four nucleotides, (p)A(p)A(p)T(p)T. The most striking feature of the sequence is its symmetry.