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Updated: Jul 10, 2026

Precise Phage Mutagenesis with NgTET-Assisted CRISPR-Cas Systems
Published on: October 14, 2025
A hexanucleotide sequence (dC1-dC6 tract) restricts the dC-specific cleavage of single-stranded DNA by endonuclease
Hiroyuki Ohshima1, Nobutaka Hirano, Hideo Takahashi
1Department of Applied Biological Science, Nihon University College of Bioresource Sciences, Fujisawa-shi, Kanagawa 252-8510, Japan.
Abstract:
Endonuclease (Endo) IV encoded by denB of bacteriophage T4 is an enzyme that cleaves single-stranded (ss) DNA in a dC-specific manner. Previously we have demonstrated that a dTdCdA is most preferable for Endo IV when an oligonucleotide substrate having a single dC residue is used. Here we demonstrate that Endo IV cleaves ssDNAs exclusively at the 5'-proximal dC where a sequence comprises dC residues both at the 5' proximal and 3' proximal positions (a dCs tract-dependent cleavage). The dCs tract-dependent cleavage is efficient and occurs when a dCs tract has at least 6 bases. Some dCs tracts larger than 6 bases behave as that of 6 bases (an extended dCs tract), while some others do not. One decameric dCs tract was shown to be cleavable in a dCs tract-dependent manner, but that with 13 dCs was not. The dCs tract-dependent cleavage is enhanced by the presence of a third dC residue at least for a 6 or 7 dCs tract. In contrast to the dCs tract-dependent cleavage, a dCs tract-independent one is generally inefficient and if two modes are possible for a substrate DNA, a dCs tract-dependent mode prevails. A model for the dCs tract-dependent cleavage is proposed.
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