The nucleotide sequences recognized by endonucleases AvaI and AvaII from Anabaena variabilis

Abstract

Determination of the 5''-terminal sequences flanking all the individual cleavage sites for endonuclease AvaI in bacteriophage-.lambda. DNA showed that this enzyme recognizes the hexanucleotide sequence: .**GRAPHIC**. This sequence is cut as shown by the arrows to give single-stranded 5''-tetranucleotide protrusions (cohesive ends). Endonucleases SmaI, XhoI and XmaI recognize different symmetrical subsets of this sequence and provide independent evidence for the occurrence of these subsets at particular endonuclease-AvaI cleavage sites in the bacteriophage-.lambda. genome. Further evidence for this structure came from the demonstration that DNA fragments generated by endonuclease AvaI can be ligated to form a discrete set of larger molecules and from nearest-neighbor analysis, which showed that cytosine residues occurred at the 3''-side of cleavage points. The observation that endonuclease AvaII recognized a subset of the sites recognized by AsuI led to the deduction that AvaII recognizes the pentanucleotide sequence: .**GRAPHIC**. and breaks internucleotide bonds at the positions indicated by the arrows.