Preparation and specificity of endonuclease IV induced by bacteriophage T4.

Bacteriophage-T4-induced endonuclease IV suitable for DNA sequence analysis has been prepared by a modified and easily reproducible method. The specificity of T4-induced endonuclease IV has been investigated in order to verify whether this enzyme exhibits a single nucleotide recognition or a short sequence recognition. The 5'-terminal dinucleotides and 3'-terminal nucleotides of oligonucleotides released by T4-induced endonuclease IV from three single-stranded DNAs (from bacteriophages phiX174, fd, M 13) have been analysed. In different DNAs, 74-82% of the 5'-terminal dinucleotides end in 5'-deoxycytidylic acid; small but significant levels of several dinucleotides ending in 5'-deoxyadenylic acid, 5'-thymidylic acid and 5'-deoxyguanylic acid are also found. As far as 3'-terminal nucleotides are concerned all nucleotides are present with a large predominance of thymidylic acid. It is concluded that T4-induced endonuclease IV recognizes short nucleotide sequences like all other DNases investigated so far. The spectrum of such sequences is, however, very narrow.